Moved, renamed, and deleted files

The original directory structure was scattered and unorganized.
Changes are basically to make it look like kernel structure.

2 files changed, 1103 insertions, 0 deletions

diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
new file mode 100644
index 00000000..39809035
--- /dev/null
+++ b/drivers/lguest/x86/core.c
@@ -0,0 +1,715 @@
+/*
+ * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
+ * Copyright (C) 2007, Jes Sorensen <jes@sgi.com> SGI.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ * NON INFRINGEMENT.  See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+/*P:450
+ * This file contains the x86-specific lguest code.  It used to be all
+ * mixed in with drivers/lguest/core.c but several foolhardy code slashers
+ * wrestled most of the dependencies out to here in preparation for porting
+ * lguest to other architectures (see what I mean by foolhardy?).
+ *
+ * This also contains a couple of non-obvious setup and teardown pieces which
+ * were implemented after days of debugging pain.
+:*/
+#include <linux/kernel.h>
+#include <linux/start_kernel.h>
+#include <linux/string.h>
+#include <linux/console.h>
+#include <linux/screen_info.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/cpu.h>
+#include <linux/lguest.h>
+#include <linux/lguest_launcher.h>
+#include <asm/paravirt.h>
+#include <asm/param.h>
+#include <asm/page.h>
+#include <asm/pgtable.h>
+#include <asm/desc.h>
+#include <asm/setup.h>
+#include <asm/lguest.h>
+#include <asm/uaccess.h>
+#include <asm/i387.h>
+#include "../lg.h"
+
+static int cpu_had_pge;
+
+static struct {
+	unsigned long offset;
+	unsigned short segment;
+} lguest_entry;
+
+/* Offset from where switcher.S was compiled to where we've copied it */
+static unsigned long switcher_offset(void)
+{
+	return SWITCHER_ADDR - (unsigned long)start_switcher_text;
+}
+
+/* This cpu's struct lguest_pages. */
+static struct lguest_pages *lguest_pages(unsigned int cpu)
+{
+	return &(((struct lguest_pages *)
+		  (SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
+}
+
+static DEFINE_PER_CPU(struct lg_cpu *, lg_last_cpu);
+
+/*S:010
+ * We approach the Switcher.
+ *
+ * Remember that each CPU has two pages which are visible to the Guest when it
+ * runs on that CPU.  This has to contain the state for that Guest: we copy the
+ * state in just before we run the Guest.
+ *
+ * Each Guest has "changed" flags which indicate what has changed in the Guest
+ * since it last ran.  We saw this set in interrupts_and_traps.c and
+ * segments.c.
+ */
+static void copy_in_guest_info(struct lg_cpu *cpu, struct lguest_pages *pages)
+{
+	/*
+	 * Copying all this data can be quite expensive.  We usually run the
+	 * same Guest we ran last time (and that Guest hasn't run anywhere else
+	 * meanwhile).  If that's not the case, we pretend everything in the
+	 * Guest has changed.
+	 */
+	if (__this_cpu_read(lg_last_cpu) != cpu || cpu->last_pages != pages) {
+		__this_cpu_write(lg_last_cpu, cpu);
+		cpu->last_pages = pages;
+		cpu->changed = CHANGED_ALL;
+	}
+
+	/*
+	 * These copies are pretty cheap, so we do them unconditionally: */
+	/* Save the current Host top-level page directory.
+	 */
+	pages->state.host_cr3 = __pa(current->mm->pgd);
+	/*
+	 * Set up the Guest's page tables to see this CPU's pages (and no
+	 * other CPU's pages).
+	 */
+	map_switcher_in_guest(cpu, pages);
+	/*
+	 * Set up the two "TSS" members which tell the CPU what stack to use
+	 * for traps which do directly into the Guest (ie. traps at privilege
+	 * level 1).
+	 */
+	pages->state.guest_tss.sp1 = cpu->esp1;
+	pages->state.guest_tss.ss1 = cpu->ss1;
+
+	/* Copy direct-to-Guest trap entries. */
+	if (cpu->changed & CHANGED_IDT)
+		copy_traps(cpu, pages->state.guest_idt, default_idt_entries);
+
+	/* Copy all GDT entries which the Guest can change. */
+	if (cpu->changed & CHANGED_GDT)
+		copy_gdt(cpu, pages->state.guest_gdt);
+	/* If only the TLS entries have changed, copy them. */
+	else if (cpu->changed & CHANGED_GDT_TLS)
+		copy_gdt_tls(cpu, pages->state.guest_gdt);
+
+	/* Mark the Guest as unchanged for next time. */
+	cpu->changed = 0;
+}
+
+/* Finally: the code to actually call into the Switcher to run the Guest. */
+static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages)
+{
+	/* This is a dummy value we need for GCC's sake. */
+	unsigned int clobber;
+
+	/*
+	 * Copy the guest-specific information into this CPU's "struct
+	 * lguest_pages".
+	 */
+	copy_in_guest_info(cpu, pages);
+
+	/*
+	 * Set the trap number to 256 (impossible value).  If we fault while
+	 * switching to the Guest (bad segment registers or bug), this will
+	 * cause us to abort the Guest.
+	 */
+	cpu->regs->trapnum = 256;
+
+	/*
+	 * Now: we push the "eflags" register on the stack, then do an "lcall".
+	 * This is how we change from using the kernel code segment to using
+	 * the dedicated lguest code segment, as well as jumping into the
+	 * Switcher.
+	 *
+	 * The lcall also pushes the old code segment (KERNEL_CS) onto the
+	 * stack, then the address of this call.  This stack layout happens to
+	 * exactly match the stack layout created by an interrupt...
+	 */
+	asm volatile("pushf; lcall *lguest_entry"
+		     /*
+		      * This is how we tell GCC that %eax ("a") and %ebx ("b")
+		      * are changed by this routine.  The "=" means output.
+		      */
+		     : "=a"(clobber), "=b"(clobber)
+		     /*
+		      * %eax contains the pages pointer.  ("0" refers to the
+		      * 0-th argument above, ie "a").  %ebx contains the
+		      * physical address of the Guest's top-level page
+		      * directory.
+		      */
+		     : "0"(pages), "1"(__pa(cpu->lg->pgdirs[cpu->cpu_pgd].pgdir))
+		     /*
+		      * We tell gcc that all these registers could change,
+		      * which means we don't have to save and restore them in
+		      * the Switcher.
+		      */
+		     : "memory", "%edx", "%ecx", "%edi", "%esi");
+}
+/*:*/
+
+/*M:002
+ * There are hooks in the scheduler which we can register to tell when we
+ * get kicked off the CPU (preempt_notifier_register()).  This would allow us
+ * to lazily disable SYSENTER which would regain some performance, and should
+ * also simplify copy_in_guest_info().  Note that we'd still need to restore
+ * things when we exit to Launcher userspace, but that's fairly easy.
+ *
+ * We could also try using these hooks for PGE, but that might be too expensive.
+ *
+ * The hooks were designed for KVM, but we can also put them to good use.
+:*/
+
+/*H:040
+ * This is the i386-specific code to setup and run the Guest.  Interrupts
+ * are disabled: we own the CPU.
+ */
+void lguest_arch_run_guest(struct lg_cpu *cpu)
+{
+	/*
+	 * Remember the awfully-named TS bit?  If the Guest has asked to set it
+	 * we set it now, so we can trap and pass that trap to the Guest if it
+	 * uses the FPU.
+	 */
+	if (cpu->ts)
+		unlazy_fpu(current);
+
+	/*
+	 * SYSENTER is an optimized way of doing system calls.  We can't allow
+	 * it because it always jumps to privilege level 0.  A normal Guest
+	 * won't try it because we don't advertise it in CPUID, but a malicious
+	 * Guest (or malicious Guest userspace program) could, so we tell the
+	 * CPU to disable it before running the Guest.
+	 */
+	if (boot_cpu_has(X86_FEATURE_SEP))
+		wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);
+
+	/*
+	 * Now we actually run the Guest.  It will return when something
+	 * interesting happens, and we can examine its registers to see what it
+	 * was doing.
+	 */
+	run_guest_once(cpu, lguest_pages(raw_smp_processor_id()));
+
+	/*
+	 * Note that the "regs" structure contains two extra entries which are
+	 * not really registers: a trap number which says what interrupt or
+	 * trap made the switcher code come back, and an error code which some
+	 * traps set.
+	 */
+
+	 /* Restore SYSENTER if it's supposed to be on. */
+	 if (boot_cpu_has(X86_FEATURE_SEP))
+		wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
+
+	/*
+	 * If the Guest page faulted, then the cr2 register will tell us the
+	 * bad virtual address.  We have to grab this now, because once we
+	 * re-enable interrupts an interrupt could fault and thus overwrite
+	 * cr2, or we could even move off to a different CPU.
+	 */
+	if (cpu->regs->trapnum == 14)
+		cpu->arch.last_pagefault = read_cr2();
+	/*
+	 * Similarly, if we took a trap because the Guest used the FPU,
+	 * we have to restore the FPU it expects to see.
+	 * math_state_restore() may sleep and we may even move off to
+	 * a different CPU. So all the critical stuff should be done
+	 * before this.
+	 */
+	else if (cpu->regs->trapnum == 7)
+		math_state_restore();
+}
+
+/*H:130
+ * Now we've examined the hypercall code; our Guest can make requests.
+ * Our Guest is usually so well behaved; it never tries to do things it isn't
+ * allowed to, and uses hypercalls instead.  Unfortunately, Linux's paravirtual
+ * infrastructure isn't quite complete, because it doesn't contain replacements
+ * for the Intel I/O instructions.  As a result, the Guest sometimes fumbles
+ * across one during the boot process as it probes for various things which are
+ * usually attached to a PC.
+ *
+ * When the Guest uses one of these instructions, we get a trap (General
+ * Protection Fault) and come here.  We see if it's one of those troublesome
+ * instructions and skip over it.  We return true if we did.
+ */
+static int emulate_insn(struct lg_cpu *cpu)
+{
+	u8 insn;
+	unsigned int insnlen = 0, in = 0, small_operand = 0;
+	/*
+	 * The eip contains the *virtual* address of the Guest's instruction:
+	 * walk the Guest's page tables to find the "physical" address.
+	 */
+	unsigned long physaddr = guest_pa(cpu, cpu->regs->eip);
+
+	/*
+	 * This must be the Guest kernel trying to do something, not userspace!
+	 * The bottom two bits of the CS segment register are the privilege
+	 * level.
+	 */
+	if ((cpu->regs->cs & 3) != GUEST_PL)
+		return 0;
+
+	/* Decoding x86 instructions is icky. */
+	insn = lgread(cpu, physaddr, u8);
+
+	/*
+	 * Around 2.6.33, the kernel started using an emulation for the
+	 * cmpxchg8b instruction in early boot on many configurations.  This
+	 * code isn't paravirtualized, and it tries to disable interrupts.
+	 * Ignore it, which will Mostly Work.
+	 */
+	if (insn == 0xfa) {
+		/* "cli", or Clear Interrupt Enable instruction.  Skip it. */
+		cpu->regs->eip++;
+		return 1;
+	}
+
+	/*
+	 * 0x66 is an "operand prefix".  It means a 16, not 32 bit in/out.
+	 */
+	if (insn == 0x66) {
+		small_operand = 1;
+		/* The instruction is 1 byte so far, read the next byte. */
+		insnlen = 1;
+		insn = lgread(cpu, physaddr + insnlen, u8);
+	}
+
+	/*
+	 * We can ignore the lower bit for the moment and decode the 4 opcodes
+	 * we need to emulate.
+	 */
+	switch (insn & 0xFE) {
+	case 0xE4: /* in     <next byte>,%al */
+		insnlen += 2;
+		in = 1;
+		break;
+	case 0xEC: /* in     (%dx),%al */
+		insnlen += 1;
+		in = 1;
+		break;
+	case 0xE6: /* out    %al,<next byte> */
+		insnlen += 2;
+		break;
+	case 0xEE: /* out    %al,(%dx) */
+		insnlen += 1;
+		break;
+	default:
+		/* OK, we don't know what this is, can't emulate. */
+		return 0;
+	}
+
+	/*
+	 * If it was an "IN" instruction, they expect the result to be read
+	 * into %eax, so we change %eax.  We always return all-ones, which
+	 * traditionally means "there's nothing there".
+	 */
+	if (in) {
+		/* Lower bit tells means it's a 32/16 bit access */
+		if (insn & 0x1) {
+			if (small_operand)
+				cpu->regs->eax |= 0xFFFF;
+			else
+				cpu->regs->eax = 0xFFFFFFFF;
+		} else
+			cpu->regs->eax |= 0xFF;
+	}
+	/* Finally, we've "done" the instruction, so move past it. */
+	cpu->regs->eip += insnlen;
+	/* Success! */
+	return 1;
+}
+
+/*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
+void lguest_arch_handle_trap(struct lg_cpu *cpu)
+{
+	switch (cpu->regs->trapnum) {
+	case 13: /* We've intercepted a General Protection Fault. */
+		/*
+		 * Check if this was one of those annoying IN or OUT
+		 * instructions which we need to emulate.  If so, we just go
+		 * back into the Guest after we've done it.
+		 */
+		if (cpu->regs->errcode == 0) {
+			if (emulate_insn(cpu))
+				return;
+		}
+		break;
+	case 14: /* We've intercepted a Page Fault. */
+		/*
+		 * The Guest accessed a virtual address that wasn't mapped.
+		 * This happens a lot: we don't actually set up most of the page
+		 * tables for the Guest at all when we start: as it runs it asks
+		 * for more and more, and we set them up as required. In this
+		 * case, we don't even tell the Guest that the fault happened.
+		 *
+		 * The errcode tells whether this was a read or a write, and
+		 * whether kernel or userspace code.
+		 */
+		if (demand_page(cpu, cpu->arch.last_pagefault,
+				cpu->regs->errcode))
+			return;
+
+		/*
+		 * OK, it's really not there (or not OK): the Guest needs to
+		 * know.  We write out the cr2 value so it knows where the
+		 * fault occurred.
+		 *
+		 * Note that if the Guest were really messed up, this could
+		 * happen before it's done the LHCALL_LGUEST_INIT hypercall, so
+		 * lg->lguest_data could be NULL
+		 */
+		if (cpu->lg->lguest_data &&
+		    put_user(cpu->arch.last_pagefault,
+			     &cpu->lg->lguest_data->cr2))
+			kill_guest(cpu, "Writing cr2");
+		break;
+	case 7: /* We've intercepted a Device Not Available fault. */
+		/*
+		 * If the Guest doesn't want to know, we already restored the
+		 * Floating Point Unit, so we just continue without telling it.
+		 */
+		if (!cpu->ts)
+			return;
+		break;
+	case 32 ... 255:
+		/*
+		 * These values mean a real interrupt occurred, in which case
+		 * the Host handler has already been run. We just do a
+		 * friendly check if another process should now be run, then
+		 * return to run the Guest again.
+		 */
+		cond_resched();
+		return;
+	case LGUEST_TRAP_ENTRY:
+		/*
+		 * Our 'struct hcall_args' maps directly over our regs: we set
+		 * up the pointer now to indicate a hypercall is pending.
+		 */
+		cpu->hcall = (struct hcall_args *)cpu->regs;
+		return;
+	}
+
+	/* We didn't handle the trap, so it needs to go to the Guest. */
+	if (!deliver_trap(cpu, cpu->regs->trapnum))
+		/*
+		 * If the Guest doesn't have a handler (either it hasn't
+		 * registered any yet, or it's one of the faults we don't let
+		 * it handle), it dies with this cryptic error message.
+		 */
+		kill_guest(cpu, "unhandled trap %li at %#lx (%#lx)",
+			   cpu->regs->trapnum, cpu->regs->eip,
+			   cpu->regs->trapnum == 14 ? cpu->arch.last_pagefault
+			   : cpu->regs->errcode);
+}
+
+/*
+ * Now we can look at each of the routines this calls, in increasing order of
+ * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
+ * deliver_trap() and demand_page().  After all those, we'll be ready to
+ * examine the Switcher, and our philosophical understanding of the Host/Guest
+ * duality will be complete.
+:*/
+static void adjust_pge(void *on)
+{
+	if (on)
+		write_cr4(read_cr4() | X86_CR4_PGE);
+	else
+		write_cr4(read_cr4() & ~X86_CR4_PGE);
+}
+
+/*H:020
+ * Now the Switcher is mapped and every thing else is ready, we need to do
+ * some more i386-specific initialization.
+ */
+void __init lguest_arch_host_init(void)
+{
+	int i;
+
+	/*
+	 * Most of the x86/switcher_32.S doesn't care that it's been moved; on
+	 * Intel, jumps are relative, and it doesn't access any references to
+	 * external code or data.
+	 *
+	 * The only exception is the interrupt handlers in switcher.S: their
+	 * addresses are placed in a table (default_idt_entries), so we need to
+	 * update the table with the new addresses.  switcher_offset() is a
+	 * convenience function which returns the distance between the
+	 * compiled-in switcher code and the high-mapped copy we just made.
+	 */
+	for (i = 0; i < IDT_ENTRIES; i++)
+		default_idt_entries[i] += switcher_offset();
+
+	/*
+	 * Set up the Switcher's per-cpu areas.
+	 *
+	 * Each CPU gets two pages of its own within the high-mapped region
+	 * (aka. "struct lguest_pages").  Much of this can be initialized now,
+	 * but some depends on what Guest we are running (which is set up in
+	 * copy_in_guest_info()).
+	 */
+	for_each_possible_cpu(i) {
+		/* lguest_pages() returns this CPU's two pages. */
+		struct lguest_pages *pages = lguest_pages(i);
+		/* This is a convenience pointer to make the code neater. */
+		struct lguest_ro_state *state = &pages->state;
+
+		/*
+		 * The Global Descriptor Table: the Host has a different one
+		 * for each CPU.  We keep a descriptor for the GDT which says
+		 * where it is and how big it is (the size is actually the last
+		 * byte, not the size, hence the "-1").
+		 */
+		state->host_gdt_desc.size = GDT_SIZE-1;
+		state->host_gdt_desc.address = (long)get_cpu_gdt_table(i);
+
+		/*
+		 * All CPUs on the Host use the same Interrupt Descriptor
+		 * Table, so we just use store_idt(), which gets this CPU's IDT
+		 * descriptor.
+		 */
+		store_idt(&state->host_idt_desc);
+
+		/*
+		 * The descriptors for the Guest's GDT and IDT can be filled
+		 * out now, too.  We copy the GDT & IDT into ->guest_gdt and
+		 * ->guest_idt before actually running the Guest.
+		 */
+		state->guest_idt_desc.size = sizeof(state->guest_idt)-1;
+		state->guest_idt_desc.address = (long)&state->guest_idt;
+		state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1;
+		state->guest_gdt_desc.address = (long)&state->guest_gdt;
+
+		/*
+		 * We know where we want the stack to be when the Guest enters
+		 * the Switcher: in pages->regs.  The stack grows upwards, so
+		 * we start it at the end of that structure.
+		 */
+		state->guest_tss.sp0 = (long)(&pages->regs + 1);
+		/*
+		 * And this is the GDT entry to use for the stack: we keep a
+		 * couple of special LGUEST entries.
+		 */
+		state->guest_tss.ss0 = LGUEST_DS;
+
+		/*
+		 * x86 can have a finegrained bitmap which indicates what I/O
+		 * ports the process can use.  We set it to the end of our
+		 * structure, meaning "none".
+		 */
+		state->guest_tss.io_bitmap_base = sizeof(state->guest_tss);
+
+		/*
+		 * Some GDT entries are the same across all Guests, so we can
+		 * set them up now.
+		 */
+		setup_default_gdt_entries(state);
+		/* Most IDT entries are the same for all Guests, too.*/
+		setup_default_idt_entries(state, default_idt_entries);
+
+		/*
+		 * The Host needs to be able to use the LGUEST segments on this
+		 * CPU, too, so put them in the Host GDT.
+		 */
+		get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
+		get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
+	}
+
+	/*
+	 * In the Switcher, we want the %cs segment register to use the
+	 * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
+	 * it will be undisturbed when we switch.  To change %cs and jump we
+	 * need this structure to feed to Intel's "lcall" instruction.
+	 */
+	lguest_entry.offset = (long)switch_to_guest + switcher_offset();
+	lguest_entry.segment = LGUEST_CS;
+
+	/*
+	 * Finally, we need to turn off "Page Global Enable".  PGE is an
+	 * optimization where page table entries are specially marked to show
+	 * they never change.  The Host kernel marks all the kernel pages this
+	 * way because it's always present, even when userspace is running.
+	 *
+	 * Lguest breaks this: unbeknownst to the rest of the Host kernel, we
+	 * switch to the Guest kernel.  If you don't disable this on all CPUs,
+	 * you'll get really weird bugs that you'll chase for two days.
+	 *
+	 * I used to turn PGE off every time we switched to the Guest and back
+	 * on when we return, but that slowed the Switcher down noticibly.
+	 */
+
+	/*
+	 * We don't need the complexity of CPUs coming and going while we're
+	 * doing this.
+	 */
+	get_online_cpus();
+	if (cpu_has_pge) { /* We have a broader idea of "global". */
+		/* Remember that this was originally set (for cleanup). */
+		cpu_had_pge = 1;
+		/*
+		 * adjust_pge is a helper function which sets or unsets the PGE
+		 * bit on its CPU, depending on the argument (0 == unset).
+		 */
+		on_each_cpu(adjust_pge, (void *)0, 1);
+		/* Turn off the feature in the global feature set. */
+		clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
+	}
+	put_online_cpus();
+}
+/*:*/
+
+void __exit lguest_arch_host_fini(void)
+{
+	/* If we had PGE before we started, turn it back on now. */
+	get_online_cpus();
+	if (cpu_had_pge) {
+		set_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
+		/* adjust_pge's argument "1" means set PGE. */
+		on_each_cpu(adjust_pge, (void *)1, 1);
+	}
+	put_online_cpus();
+}
+
+
+/*H:122 The i386-specific hypercalls simply farm out to the right functions. */
+int lguest_arch_do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
+{
+	switch (args->arg0) {
+	case LHCALL_LOAD_GDT_ENTRY:
+		load_guest_gdt_entry(cpu, args->arg1, args->arg2, args->arg3);
+		break;
+	case LHCALL_LOAD_IDT_ENTRY:
+		load_guest_idt_entry(cpu, args->arg1, args->arg2, args->arg3);
+		break;
+	case LHCALL_LOAD_TLS:
+		guest_load_tls(cpu, args->arg1);
+		break;
+	default:
+		/* Bad Guest.  Bad! */
+		return -EIO;
+	}
+	return 0;
+}
+
+/*H:126 i386-specific hypercall initialization: */
+int lguest_arch_init_hypercalls(struct lg_cpu *cpu)
+{
+	u32 tsc_speed;
+
+	/*
+	 * The pointer to the Guest's "struct lguest_data" is the only argument.
+	 * We check that address now.
+	 */
+	if (!lguest_address_ok(cpu->lg, cpu->hcall->arg1,
+			       sizeof(*cpu->lg->lguest_data)))
+		return -EFAULT;
+
+	/*
+	 * Having checked it, we simply set lg->lguest_data to point straight
+	 * into the Launcher's memory at the right place and then use
+	 * copy_to_user/from_user from now on, instead of lgread/write.  I put
+	 * this in to show that I'm not immune to writing stupid
+	 * optimizations.
+	 */
+	cpu->lg->lguest_data = cpu->lg->mem_base + cpu->hcall->arg1;
+
+	/*
+	 * We insist that the Time Stamp Counter exist and doesn't change with
+	 * cpu frequency.  Some devious chip manufacturers decided that TSC
+	 * changes could be handled in software.  I decided that time going
+	 * backwards might be good for benchmarks, but it's bad for users.
+	 *
+	 * We also insist that the TSC be stable: the kernel detects unreliable
+	 * TSCs for its own purposes, and we use that here.
+	 */
+	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable())
+		tsc_speed = tsc_khz;
+	else
+		tsc_speed = 0;
+	if (put_user(tsc_speed, &cpu->lg->lguest_data->tsc_khz))
+		return -EFAULT;
+
+	/* The interrupt code might not like the system call vector. */
+	if (!check_syscall_vector(cpu->lg))
+		kill_guest(cpu, "bad syscall vector");
+
+	return 0;
+}
+/*:*/
+
+/*L:030
+ * Most of the Guest's registers are left alone: we used get_zeroed_page() to
+ * allocate the structure, so they will be 0.
+ */
+void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start)
+{
+	struct lguest_regs *regs = cpu->regs;
+
+	/*
+	 * There are four "segment" registers which the Guest needs to boot:
+	 * The "code segment" register (cs) refers to the kernel code segment
+	 * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
+	 * refer to the kernel data segment __KERNEL_DS.
+	 *
+	 * The privilege level is packed into the lower bits.  The Guest runs
+	 * at privilege level 1 (GUEST_PL).
+	 */
+	regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
+	regs->cs = __KERNEL_CS|GUEST_PL;
+
+	/*
+	 * The "eflags" register contains miscellaneous flags.  Bit 1 (0x002)
+	 * is supposed to always be "1".  Bit 9 (0x200) controls whether
+	 * interrupts are enabled.  We always leave interrupts enabled while
+	 * running the Guest.
+	 */
+	regs->eflags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
+
+	/*
+	 * The "Extended Instruction Pointer" register says where the Guest is
+	 * running.
+	 */
+	regs->eip = start;
+
+	/*
+	 * %esi points to our boot information, at physical address 0, so don't
+	 * touch it.
+	 */
+
+	/* There are a couple of GDT entries the Guest expects at boot. */
+	setup_guest_gdt(cpu);
+}
diff --git a/drivers/lguest/x86/switcher_32.S b/drivers/lguest/x86/switcher_32.S
new file mode 100644
index 00000000..40634b0d
--- /dev/null
+++ b/drivers/lguest/x86/switcher_32.S
@@ -0,0 +1,388 @@
+/*P:900
+ * This is the Switcher: code which sits at 0xFFC00000 (or 0xFFE00000) astride
+ * both the Host and Guest to do the low-level Guest<->Host switch.  It is as
+ * simple as it can be made, but it's naturally very specific to x86.
+ *
+ * You have now completed Preparation.  If this has whet your appetite; if you
+ * are feeling invigorated and refreshed then the next, more challenging stage
+ * can be found in "make Guest".
+ :*/
+
+/*M:012
+ * Lguest is meant to be simple: my rule of thumb is that 1% more LOC must
+ * gain at least 1% more performance.  Since neither LOC nor performance can be
+ * measured beforehand, it generally means implementing a feature then deciding
+ * if it's worth it.  And once it's implemented, who can say no?
+ *
+ * This is why I haven't implemented this idea myself.  I want to, but I
+ * haven't.  You could, though.
+ *
+ * The main place where lguest performance sucks is Guest page faulting.  When
+ * a Guest userspace process hits an unmapped page we switch back to the Host,
+ * walk the page tables, find it's not mapped, switch back to the Guest page
+ * fault handler, which calls a hypercall to set the page table entry, then
+ * finally returns to userspace.  That's two round-trips.
+ *
+ * If we had a small walker in the Switcher, we could quickly check the Guest
+ * page table and if the page isn't mapped, immediately reflect the fault back
+ * into the Guest.  This means the Switcher would have to know the top of the
+ * Guest page table and the page fault handler address.
+ *
+ * For simplicity, the Guest should only handle the case where the privilege
+ * level of the fault is 3 and probably only not present or write faults.  It
+ * should also detect recursive faults, and hand the original fault to the
+ * Host (which is actually really easy).
+ *
+ * Two questions remain.  Would the performance gain outweigh the complexity?
+ * And who would write the verse documenting it?
+:*/
+
+/*M:011
+ * Lguest64 handles NMI.  This gave me NMI envy (until I looked at their
+ * code).  It's worth doing though, since it would let us use oprofile in the
+ * Host when a Guest is running.
+:*/
+
+/*S:100
+ * Welcome to the Switcher itself!
+ *
+ * This file contains the low-level code which changes the CPU to run the Guest
+ * code, and returns to the Host when something happens.  Understand this, and
+ * you understand the heart of our journey.
+ *
+ * Because this is in assembler rather than C, our tale switches from prose to
+ * verse.  First I tried limericks:
+ *
+ *	There once was an eax reg,
+ *	To which our pointer was fed,
+ *	It needed an add,
+ *	Which asm-offsets.h had
+ *	But this limerick is hurting my head.
+ *
+ * Next I tried haikus, but fitting the required reference to the seasons in
+ * every stanza was quickly becoming tiresome:
+ *
+ *	The %eax reg
+ *	Holds "struct lguest_pages" now:
+ *	Cherry blossoms fall.
+ *
+ * Then I started with Heroic Verse, but the rhyming requirement leeched away
+ * the content density and led to some uniquely awful oblique rhymes:
+ *
+ *	These constants are coming from struct offsets
+ *	For use within the asm switcher text.
+ *
+ * Finally, I settled for something between heroic hexameter, and normal prose
+ * with inappropriate linebreaks.  Anyway, it aint no Shakespeare.
+ */
+
+// Not all kernel headers work from assembler
+// But these ones are needed: the ENTRY() define
+// And constants extracted from struct offsets
+// To avoid magic numbers and breakage:
+// Should they change the compiler can't save us
+// Down here in the depths of assembler code.
+#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
+#include <asm/page.h>
+#include <asm/segment.h>
+#include <asm/lguest.h>
+
+// We mark the start of the code to copy
+// It's placed in .text tho it's never run here
+// You'll see the trick macro at the end
+// Which interleaves data and text to effect.
+.text
+ENTRY(start_switcher_text)
+
+// When we reach switch_to_guest we have just left
+// The safe and comforting shores of C code
+// %eax has the "struct lguest_pages" to use
+// Where we save state and still see it from the Guest
+// And %ebx holds the Guest shadow pagetable:
+// Once set we have truly left Host behind.
+ENTRY(switch_to_guest)
+	// We told gcc all its regs could fade,
+	// Clobbered by our journey into the Guest
+	// We could have saved them, if we tried
+	// But time is our master and cycles count.
+
+	// Segment registers must be saved for the Host
+	// We push them on the Host stack for later
+	pushl	%es
+	pushl	%ds
+	pushl	%gs
+	pushl	%fs
+	// But the compiler is fickle, and heeds
+	// No warning of %ebp clobbers
+	// When frame pointers are used.  That register
+	// Must be saved and restored or chaos strikes.
+	pushl	%ebp
+	// The Host's stack is done, now save it away
+	// In our "struct lguest_pages" at offset
+	// Distilled into asm-offsets.h
+	movl	%esp, LGUEST_PAGES_host_sp(%eax)
+
+	// All saved and there's now five steps before us:
+	// Stack, GDT, IDT, TSS
+	// Then last of all the page tables are flipped.
+
+	// Yet beware that our stack pointer must be
+	// Always valid lest an NMI hits
+	// %edx does the duty here as we juggle
+	// %eax is lguest_pages: our stack lies within.
+	movl	%eax, %edx
+	addl	$LGUEST_PAGES_regs, %edx
+	movl	%edx, %esp
+
+	// The Guest's GDT we so carefully
+	// Placed in the "struct lguest_pages" before
+	lgdt	LGUEST_PAGES_guest_gdt_desc(%eax)
+
+	// The Guest's IDT we did partially
+	// Copy to "struct lguest_pages" as well.
+	lidt	LGUEST_PAGES_guest_idt_desc(%eax)
+
+	// The TSS entry which controls traps
+	// Must be loaded up with "ltr" now:
+	// The GDT entry that TSS uses 
+	// Changes type when we load it: damn Intel!
+	// For after we switch over our page tables
+	// That entry will be read-only: we'd crash.
+	movl	$(GDT_ENTRY_TSS*8), %edx
+	ltr	%dx
+
+	// Look back now, before we take this last step!
+	// The Host's TSS entry was also marked used;
+	// Let's clear it again for our return.
+	// The GDT descriptor of the Host
+	// Points to the table after two "size" bytes
+	movl	(LGUEST_PAGES_host_gdt_desc+2)(%eax), %edx
+	// Clear "used" from type field (byte 5, bit 2)
+	andb	$0xFD, (GDT_ENTRY_TSS*8 + 5)(%edx)
+
+	// Once our page table's switched, the Guest is live!
+	// The Host fades as we run this final step.
+	// Our "struct lguest_pages" is now read-only.
+	movl	%ebx, %cr3
+
+	// The page table change did one tricky thing:
+	// The Guest's register page has been mapped
+	// Writable under our %esp (stack) --
+	// We can simply pop off all Guest regs.
+	popl	%eax
+	popl	%ebx
+	popl	%ecx
+	popl	%edx
+	popl	%esi
+	popl	%edi
+	popl	%ebp
+	popl	%gs
+	popl	%fs
+	popl	%ds
+	popl	%es
+
+	// Near the base of the stack lurk two strange fields
+	// Which we fill as we exit the Guest
+	// These are the trap number and its error
+	// We can simply step past them on our way.
+	addl	$8, %esp
+
+	// The last five stack slots hold return address
+	// And everything needed to switch privilege
+	// From Switcher's level 0 to Guest's 1,
+	// And the stack where the Guest had last left it.
+	// Interrupts are turned back on: we are Guest.
+	iret
+
+// We tread two paths to switch back to the Host
+// Yet both must save Guest state and restore Host
+// So we put the routine in a macro.
+#define SWITCH_TO_HOST							\
+	/* We save the Guest state: all registers first			\
+	 * Laid out just as "struct lguest_regs" defines */		\
+	pushl	%es;							\
+	pushl	%ds;							\
+	pushl	%fs;							\
+	pushl	%gs;							\
+	pushl	%ebp;							\
+	pushl	%edi;							\
+	pushl	%esi;							\
+	pushl	%edx;							\
+	pushl	%ecx;							\
+	pushl	%ebx;							\
+	pushl	%eax;							\
+	/* Our stack and our code are using segments			\
+	 * Set in the TSS and IDT					\
+	 * Yet if we were to touch data we'd use			\
+	 * Whatever data segment the Guest had.				\
+	 * Load the lguest ds segment for now. */			\
+	movl	$(LGUEST_DS), %eax;					\
+	movl	%eax, %ds;						\
+	/* So where are we?  Which CPU, which struct?			\
+	 * The stack is our clue: our TSS starts			\
+	 * It at the end of "struct lguest_pages".			\
+	 * Or we may have stumbled while restoring			\
+	 * Our Guest segment regs while in switch_to_guest,		\
+	 * The fault pushed atop that part-unwound stack.		\
+	 * If we round the stack down to the page start			\
+	 * We're at the start of "struct lguest_pages". */		\
+	movl	%esp, %eax;						\
+	andl	$(~(1 << PAGE_SHIFT - 1)), %eax;			\
+	/* Save our trap number: the switch will obscure it		\
+	 * (In the Host the Guest regs are not mapped here)		\
+	 * %ebx holds it safe for deliver_to_host */			\
+	movl	LGUEST_PAGES_regs_trapnum(%eax), %ebx;			\
+	/* The Host GDT, IDT and stack!					\
+	 * All these lie safely hidden from the Guest:			\
+	 * We must return to the Host page tables			\
+	 * (Hence that was saved in struct lguest_pages) */		\
+	movl	LGUEST_PAGES_host_cr3(%eax), %edx;			\
+	movl	%edx, %cr3;						\
+	/* As before, when we looked back at the Host			\
+	 * As we left and marked TSS unused				\
+	 * So must we now for the Guest left behind. */			\
+	andb	$0xFD, (LGUEST_PAGES_guest_gdt+GDT_ENTRY_TSS*8+5)(%eax); \
+	/* Switch to Host's GDT, IDT. */				\
+	lgdt	LGUEST_PAGES_host_gdt_desc(%eax);			\
+	lidt	LGUEST_PAGES_host_idt_desc(%eax);			\
+	/* Restore the Host's stack where its saved regs lie */		\
+	movl	LGUEST_PAGES_host_sp(%eax), %esp;			\
+	/* Last the TSS: our Host is returned */			\
+	movl	$(GDT_ENTRY_TSS*8), %edx;				\
+	ltr	%dx;							\
+	/* Restore now the regs saved right at the first. */		\
+	popl	%ebp;							\
+	popl	%fs;							\
+	popl	%gs;							\
+	popl	%ds;							\
+	popl	%es
+
+// The first path is trod when the Guest has trapped:
+// (Which trap it was has been pushed on the stack).
+// We need only switch back, and the Host will decode
+// Why we came home, and what needs to be done.
+return_to_host:
+	SWITCH_TO_HOST
+	iret
+
+// We are lead to the second path like so:
+// An interrupt, with some cause external
+// Has ajerked us rudely from the Guest's code
+// Again we must return home to the Host
+deliver_to_host:
+	SWITCH_TO_HOST
+	// But now we must go home via that place
+	// Where that interrupt was supposed to go
+	// Had we not been ensconced, running the Guest.
+	// Here we see the trickness of run_guest_once():
+	// The Host stack is formed like an interrupt
+	// With EIP, CS and EFLAGS layered.
+	// Interrupt handlers end with "iret"
+	// And that will take us home at long long last.
+
+	// But first we must find the handler to call!
+	// The IDT descriptor for the Host
+	// Has two bytes for size, and four for address:
+	// %edx will hold it for us for now.
+	movl	(LGUEST_PAGES_host_idt_desc+2)(%eax), %edx
+	// We now know the table address we need,
+	// And saved the trap's number inside %ebx.
+	// Yet the pointer to the handler is smeared
+	// Across the bits of the table entry.
+	// What oracle can tell us how to extract
+	// From such a convoluted encoding?
+	// I consulted gcc, and it gave
+	// These instructions, which I gladly credit:
+	leal	(%edx,%ebx,8), %eax
+	movzwl	(%eax),%edx
+	movl	4(%eax), %eax
+	xorw	%ax, %ax
+	orl	%eax, %edx
+	// Now the address of the handler's in %edx
+	// We call it now: its "iret" drops us home.
+	jmp	*%edx
+
+// Every interrupt can come to us here
+// But we must truly tell each apart.
+// They number two hundred and fifty six
+// And each must land in a different spot,
+// Push its number on stack, and join the stream.
+
+// And worse, a mere six of the traps stand apart
+// And push on their stack an addition:
+// An error number, thirty two bits long
+// So we punish the other two fifty
+// And make them push a zero so they match.
+
+// Yet two fifty six entries is long
+// And all will look most the same as the last
+// So we create a macro which can make
+// As many entries as we need to fill.
+
+// Note the change to .data then .text:
+// We plant the address of each entry
+// Into a (data) table for the Host
+// To know where each Guest interrupt should go.
+.macro IRQ_STUB N TARGET
+	.data; .long 1f; .text; 1:
+ // Trap eight, ten through fourteen and seventeen
+ // Supply an error number.  Else zero.
+ .if (\N <> 8) && (\N < 10 || \N > 14) && (\N <> 17)
+	pushl	$0
+ .endif
+	pushl	$\N
+	jmp	\TARGET
+	ALIGN
+.endm
+
+// This macro creates numerous entries
+// Using GAS macros which out-power C's.
+.macro IRQ_STUBS FIRST LAST TARGET
+ irq=\FIRST
+ .rept \LAST-\FIRST+1
+	IRQ_STUB irq \TARGET
+  irq=irq+1
+ .endr
+.endm
+
+// Here's the marker for our pointer table
+// Laid in the data section just before
+// Each macro places the address of code
+// Forming an array: each one points to text
+// Which handles interrupt in its turn.
+.data
+.global default_idt_entries
+default_idt_entries:
+.text
+	// The first two traps go straight back to the Host
+	IRQ_STUBS 0 1 return_to_host
+	// We'll say nothing, yet, about NMI
+	IRQ_STUB 2 handle_nmi
+	// Other traps also return to the Host
+	IRQ_STUBS 3 31 return_to_host
+	// All interrupts go via their handlers
+	IRQ_STUBS 32 127 deliver_to_host
+	// 'Cept system calls coming from userspace
+	// Are to go to the Guest, never the Host.
+	IRQ_STUB 128 return_to_host
+	IRQ_STUBS 129 255 deliver_to_host
+
+// The NMI, what a fabulous beast
+// Which swoops in and stops us no matter that
+// We're suspended between heaven and hell,
+// (Or more likely between the Host and Guest)
+// When in it comes!  We are dazed and confused
+// So we do the simplest thing which one can.
+// Though we've pushed the trap number and zero
+// We discard them, return, and hope we live.
+handle_nmi:
+	addl	$8, %esp
+	iret
+
+// We are done; all that's left is Mastery
+// And "make Mastery" is a journey long
+// Designed to make your fingers itch to code.
+
+// Here ends the text, the file and poem.
+ENTRY(end_switcher_text)