Merge git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus:
  lguest: Fix in/out emulation
  lguest: Fix translation count about wikipedia's cpuid page
  lguest: Fix three simple typos in comments
  lguest: update comments
  lguest: Simplify device initialization.
  lguest: don't rewrite vmcall instructions
  lguest: remove remaining vmcall
  lguest: use a special 1:1 linear pagetable mode until first switch.
  lguest: Do not exit on non-fatal errors

7 files changed, 140 insertions, 317 deletions

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index efa202499e37..2535933c49f8 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -117,7 +117,7 @@ static __init int map_switcher(void)
 
 	/*
 	 * Now the Switcher is mapped at the right address, we can't fail!
-	 * Copy in the compiled-in Switcher code (from <arch>_switcher.S).
+	 * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
 	 */
 	memcpy(switcher_vma->addr, start_switcher_text,
 	       end_switcher_text - start_switcher_text);
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index daaf86631647..28433a155d67 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -375,11 +375,9 @@ static bool direct_trap(unsigned int num)
 	/*
 	 * The Host needs to see page faults (for shadow paging and to save the
 	 * fault address), general protection faults (in/out emulation) and
-	 * device not available (TS handling), invalid opcode fault (kvm hcall),
-	 * and of course, the hypercall trap.
+	 * device not available (TS handling) and of course, the hypercall trap.
 	 */
-	return num != 14 && num != 13 && num != 7 &&
-			num != 6 && num != LGUEST_TRAP_ENTRY;
+	return num != 14 && num != 13 && num != 7 && num != LGUEST_TRAP_ENTRY;
 }
 /*:*/
 
@@ -429,8 +427,8 @@ void pin_stack_pages(struct lg_cpu *cpu)
 
 /*
  * Direct traps also mean that we need to know whenever the Guest wants to use
- * a different kernel stack, so we can change the IDT entries to use that
- * stack.  The IDT entries expect a virtual address, so unlike most addresses
+ * a different kernel stack, so we can change the guest TSS to use that
+ * stack.  The TSS entries expect a virtual address, so unlike most addresses
  * the Guest gives us, the "esp" (stack pointer) value here is virtual, not
  * physical.
  *
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 9136411fadd5..295df06e6590 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -59,6 +59,8 @@ struct lg_cpu {
 
 	struct lguest_pages *last_pages;
 
+	/* Initialization mode: linear map everything. */
+	bool linear_pages;
 	int cpu_pgd; /* Which pgd this cpu is currently using */
 
 	/* If a hypercall was asked for, this points to the arguments. */
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 69c84a1d88ea..5289ffa2e500 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -109,6 +109,17 @@ static u32 lg_get_features(struct virtio_device *vdev)
 }
 
 /*
+ * To notify on reset or feature finalization, we (ab)use the NOTIFY
+ * hypercall, with the descriptor address of the device.
+ */
+static void status_notify(struct virtio_device *vdev)
+{
+	unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
+
+	hcall(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset, 0, 0, 0);
+}
+
+/*
  * The virtio core takes the features the Host offers, and copies the ones
  * supported by the driver into the vdev->features array.  Once that's all
  * sorted out, this routine is called so we can tell the Host which features we
@@ -135,6 +146,9 @@ static void lg_finalize_features(struct virtio_device *vdev)
 		if (test_bit(i, vdev->features))
 			out_features[i / 8] |= (1 << (i % 8));
 	}
+
+	/* Tell Host we've finished with this device's feature negotiation */
+	status_notify(vdev);
 }
 
 /* Once they've found a field, getting a copy of it is easy. */
@@ -168,28 +182,21 @@ static u8 lg_get_status(struct virtio_device *vdev)
 	return to_lgdev(vdev)->desc->status;
 }
 
-/*
- * To notify on status updates, we (ab)use the NOTIFY hypercall, with the
- * descriptor address of the device.  A zero status means "reset".
- */
-static void set_status(struct virtio_device *vdev, u8 status)
-{
-	unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
-
-	/* We set the status. */
-	to_lgdev(vdev)->desc->status = status;
-	hcall(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset, 0, 0, 0);
-}
-
 static void lg_set_status(struct virtio_device *vdev, u8 status)
 {
 	BUG_ON(!status);
-	set_status(vdev, status);
+	to_lgdev(vdev)->desc->status = status;
+
+	/* Tell Host immediately if we failed. */
+	if (status & VIRTIO_CONFIG_S_FAILED)
+		status_notify(vdev);
 }
 
 static void lg_reset(struct virtio_device *vdev)
 {
-	set_status(vdev, 0);
+	/* 0 status means "reset" */
+	to_lgdev(vdev)->desc->status = 0;
+	status_notify(vdev);
 }
 
 /*
diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 948c547b8e9e..f97e625241ad 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -1,8 +1,10 @@
-/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
- * controls and communicates with the Guest.  For example, the first write will
- * tell us the Guest's memory layout and entry point.  A read will run the
- * Guest until something happens, such as a signal or the Guest doing a NOTIFY
- * out to the Launcher.
+/*P:200 This contains all the /dev/lguest code, whereby the userspace
+ * launcher controls and communicates with the Guest.  For example,
+ * the first write will tell us the Guest's memory layout and entry
+ * point.  A read will run the Guest until something happens, such as
+ * a signal or the Guest doing a NOTIFY out to the Launcher.  There is
+ * also a way for the Launcher to attach eventfds to particular NOTIFY
+ * values instead of returning from the read() call.
 :*/
 #include <linux/uaccess.h>
 #include <linux/miscdevice.h>
@@ -357,8 +359,8 @@ static int initialize(struct file *file, const unsigned long __user *input)
 		goto free_eventfds;
 
 	/*
-	 * Initialize the Guest's shadow page tables, using the toplevel
-	 * address the Launcher gave us.  This allocates memory, so can fail.
+	 * Initialize the Guest's shadow page tables.  This allocates
+	 * memory, so can fail.
 	 */
 	err = init_guest_pagetable(lg);
 	if (err)
@@ -516,6 +518,7 @@ static const struct file_operations lguest_fops = {
 	.read	 = read,
 	.llseek  = default_llseek,
 };
+/*:*/
 
 /*
  * This is a textbook example of a "misc" character device.  Populate a "struct
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index d21578ee95de..3b62be160a6e 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -17,7 +17,6 @@
 #include <linux/percpu.h>
 #include <asm/tlbflush.h>
 #include <asm/uaccess.h>
-#include <asm/bootparam.h>
 #include "lg.h"
 
 /*M:008
@@ -156,7 +155,7 @@ static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
 }
 
 /*
- * These functions are just like the above two, except they access the Guest
+ * These functions are just like the above, except they access the Guest
  * page tables.  Hence they return a Guest address.
  */
 static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
@@ -196,7 +195,7 @@ static unsigned long gpte_addr(struct lg_cpu *cpu,
 #endif
 /*:*/
 
-/*M:014
+/*M:007
  * get_pfn is slow: we could probably try to grab batches of pages here as
  * an optimization (ie. pre-faulting).
 :*/
@@ -325,10 +324,15 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 #endif
 
 	/* First step: get the top-level Guest page table entry. */
-	gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
-	/* Toplevel not present?  We can't map it in. */
-	if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
-		return false;
+	if (unlikely(cpu->linear_pages)) {
+		/* Faking up a linear mapping. */
+		gpgd = __pgd(CHECK_GPGD_MASK);
+	} else {
+		gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
+		/* Toplevel not present?  We can't map it in. */
+		if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
+			return false;
+	}
 
 	/* Now look at the matching shadow entry. */
 	spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
@@ -353,10 +357,15 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 	}
 
 #ifdef CONFIG_X86_PAE
-	gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
-	/* Middle level not present?  We can't map it in. */
-	if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
-		return false;
+	if (unlikely(cpu->linear_pages)) {
+		/* Faking up a linear mapping. */
+		gpmd = __pmd(_PAGE_TABLE);
+	} else {
+		gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
+		/* Middle level not present?  We can't map it in. */
+		if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
+			return false;
+	}
 
 	/* Now look at the matching shadow entry. */
 	spmd = spmd_addr(cpu, *spgd, vaddr);
@@ -397,8 +406,13 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 	gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
 #endif
 
-	/* Read the actual PTE value. */
-	gpte = lgread(cpu, gpte_ptr, pte_t);
+	if (unlikely(cpu->linear_pages)) {
+		/* Linear?  Make up a PTE which points to same page. */
+		gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
+	} else {
+		/* Read the actual PTE value. */
+		gpte = lgread(cpu, gpte_ptr, pte_t);
+	}
 
 	/* If this page isn't in the Guest page tables, we can't page it in. */
 	if (!(pte_flags(gpte) & _PAGE_PRESENT))
@@ -454,7 +468,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 	 * Finally, we write the Guest PTE entry back: we've set the
 	 * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
 	 */
-	lgwrite(cpu, gpte_ptr, pte_t, gpte);
+	if (likely(!cpu->linear_pages))
+		lgwrite(cpu, gpte_ptr, pte_t, gpte);
 
 	/*
 	 * The fault is fixed, the page table is populated, the mapping
@@ -612,6 +627,11 @@ unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
 #ifdef CONFIG_X86_PAE
 	pmd_t gpmd;
 #endif
+
+	/* Still not set up?  Just map 1:1. */
+	if (unlikely(cpu->linear_pages))
+		return vaddr;
+
 	/* First step: get the top-level Guest page table entry. */
 	gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
 	/* Toplevel not present?  We can't map it in. */
@@ -708,32 +728,6 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
 	return next;
 }
 
-/*H:430
- * (iv) Switching page tables
- *
- * Now we've seen all the page table setting and manipulation, let's see
- * what happens when the Guest changes page tables (ie. changes the top-level
- * pgdir).  This occurs on almost every context switch.
- */
-void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
-{
-	int newpgdir, repin = 0;
-
-	/* Look to see if we have this one already. */
-	newpgdir = find_pgdir(cpu->lg, pgtable);
-	/*
-	 * If not, we allocate or mug an existing one: if it's a fresh one,
-	 * repin gets set to 1.
-	 */
-	if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
-		newpgdir = new_pgdir(cpu, pgtable, &repin);
-	/* Change the current pgd index to the new one. */
-	cpu->cpu_pgd = newpgdir;
-	/* If it was completely blank, we map in the Guest kernel stack */
-	if (repin)
-		pin_stack_pages(cpu);
-}
-
 /*H:470
  * Finally, a routine which throws away everything: all PGD entries in all
  * the shadow page tables, including the Guest's kernel mappings.  This is used
@@ -780,6 +774,44 @@ void guest_pagetable_clear_all(struct lg_cpu *cpu)
 	/* We need the Guest kernel stack mapped again. */
 	pin_stack_pages(cpu);
 }
+
+/*H:430
+ * (iv) Switching page tables
+ *
+ * Now we've seen all the page table setting and manipulation, let's see
+ * what happens when the Guest changes page tables (ie. changes the top-level
+ * pgdir).  This occurs on almost every context switch.
+ */
+void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
+{
+	int newpgdir, repin = 0;
+
+	/*
+	 * The very first time they call this, we're actually running without
+	 * any page tables; we've been making it up.  Throw them away now.
+	 */
+	if (unlikely(cpu->linear_pages)) {
+		release_all_pagetables(cpu->lg);
+		cpu->linear_pages = false;
+		/* Force allocation of a new pgdir. */
+		newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
+	} else {
+		/* Look to see if we have this one already. */
+		newpgdir = find_pgdir(cpu->lg, pgtable);
+	}
+
+	/*
+	 * If not, we allocate or mug an existing one: if it's a fresh one,
+	 * repin gets set to 1.
+	 */
+	if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
+		newpgdir = new_pgdir(cpu, pgtable, &repin);
+	/* Change the current pgd index to the new one. */
+	cpu->cpu_pgd = newpgdir;
+	/* If it was completely blank, we map in the Guest kernel stack */
+	if (repin)
+		pin_stack_pages(cpu);
+}
 /*:*/
 
 /*M:009
@@ -919,168 +951,26 @@ void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
 }
 #endif
 
-/*H:505
- * To get through boot, we construct simple identity page mappings (which
- * set virtual == physical) and linear mappings which will get the Guest far
- * enough into the boot to create its own.  The linear mapping means we
- * simplify the Guest boot, but it makes assumptions about their PAGE_OFFSET,
- * as you'll see.
- *
- * We lay them out of the way, just below the initrd (which is why we need to
- * know its size here).
- */
-static unsigned long setup_pagetables(struct lguest *lg,
-				      unsigned long mem,
-				      unsigned long initrd_size)
-{
-	pgd_t __user *pgdir;
-	pte_t __user *linear;
-	unsigned long mem_base = (unsigned long)lg->mem_base;
-	unsigned int mapped_pages, i, linear_pages;
-#ifdef CONFIG_X86_PAE
-	pmd_t __user *pmds;
-	unsigned int j;
-	pgd_t pgd;
-	pmd_t pmd;
-#else
-	unsigned int phys_linear;
-#endif
-
-	/*
-	 * We have mapped_pages frames to map, so we need linear_pages page
-	 * tables to map them.
-	 */
-	mapped_pages = mem / PAGE_SIZE;
-	linear_pages = (mapped_pages + PTRS_PER_PTE - 1) / PTRS_PER_PTE;
-
-	/* We put the toplevel page directory page at the top of memory. */
-	pgdir = (pgd_t *)(mem + mem_base - initrd_size - PAGE_SIZE);
-
-	/* Now we use the next linear_pages pages as pte pages */
-	linear = (void *)pgdir - linear_pages * PAGE_SIZE;
-
-#ifdef CONFIG_X86_PAE
-	/*
-	 * And the single mid page goes below that.  We only use one, but
-	 * that's enough to map 1G, which definitely gets us through boot.
-	 */
-	pmds = (void *)linear - PAGE_SIZE;
-#endif
-	/*
-	 * Linear mapping is easy: put every page's address into the
-	 * mapping in order.
-	 */
-	for (i = 0; i < mapped_pages; i++) {
-		pte_t pte;
-		pte = pfn_pte(i, __pgprot(_PAGE_PRESENT|_PAGE_RW|_PAGE_USER));
-		if (copy_to_user(&linear[i], &pte, sizeof(pte)) != 0)
-			return -EFAULT;
-	}
-
-#ifdef CONFIG_X86_PAE
-	/*
-	 * Make the Guest PMD entries point to the corresponding place in the
-	 * linear mapping (up to one page worth of PMD).
-	 */
-	for (i = j = 0; i < mapped_pages && j < PTRS_PER_PMD;
-	     i += PTRS_PER_PTE, j++) {
-		pmd = pfn_pmd(((unsigned long)&linear[i] - mem_base)/PAGE_SIZE,
-			      __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
-
-		if (copy_to_user(&pmds[j], &pmd, sizeof(pmd)) != 0)
-			return -EFAULT;
-	}
-
-	/* One PGD entry, pointing to that PMD page. */
-	pgd = __pgd(((unsigned long)pmds - mem_base) | _PAGE_PRESENT);
-	/* Copy it in as the first PGD entry (ie. addresses 0-1G). */
-	if (copy_to_user(&pgdir[0], &pgd, sizeof(pgd)) != 0)
-		return -EFAULT;
-	/*
-	 * And the other PGD entry to make the linear mapping at PAGE_OFFSET
-	 */
-	if (copy_to_user(&pgdir[KERNEL_PGD_BOUNDARY], &pgd, sizeof(pgd)))
-		return -EFAULT;
-#else
-	/*
-	 * The top level points to the linear page table pages above.
-	 * We setup the identity and linear mappings here.
-	 */
-	phys_linear = (unsigned long)linear - mem_base;
-	for (i = 0; i < mapped_pages; i += PTRS_PER_PTE) {
-		pgd_t pgd;
-		/*
-		 * Create a PGD entry which points to the right part of the
-		 * linear PTE pages.
-		 */
-		pgd = __pgd((phys_linear + i * sizeof(pte_t)) |
-			    (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
-
-		/*
-		 * Copy it into the PGD page at 0 and PAGE_OFFSET.
-		 */
-		if (copy_to_user(&pgdir[i / PTRS_PER_PTE], &pgd, sizeof(pgd))
-		    || copy_to_user(&pgdir[pgd_index(PAGE_OFFSET)
-					   + i / PTRS_PER_PTE],
-				    &pgd, sizeof(pgd)))
-			return -EFAULT;
-	}
-#endif
-
-	/*
-	 * We return the top level (guest-physical) address: we remember where
-	 * this is to write it into lguest_data when the Guest initializes.
-	 */
-	return (unsigned long)pgdir - mem_base;
-}
-
 /*H:500
  * (vii) Setting up the page tables initially.
  *
- * When a Guest is first created, the Launcher tells us where the toplevel of
- * its first page table is.  We set some things up here:
+ * When a Guest is first created, set initialize a shadow page table which
+ * we will populate on future faults.  The Guest doesn't have any actual
+ * pagetables yet, so we set linear_pages to tell demand_page() to fake it
+ * for the moment.
  */
 int init_guest_pagetable(struct lguest *lg)
 {
-	u64 mem;
-	u32 initrd_size;
-	struct boot_params __user *boot = (struct boot_params *)lg->mem_base;
-#ifdef CONFIG_X86_PAE
-	pgd_t *pgd;
-	pmd_t *pmd_table;
-#endif
-	/*
-	 * Get the Guest memory size and the ramdisk size from the boot header
-	 * located at lg->mem_base (Guest address 0).
-	 */
-	if (copy_from_user(&mem, &boot->e820_map[0].size, sizeof(mem))
-	    || get_user(initrd_size, &boot->hdr.ramdisk_size))
-		return -EFAULT;
+	struct lg_cpu *cpu = &lg->cpus[0];
+	int allocated = 0;
 
-	/*
-	 * We start on the first shadow page table, and give it a blank PGD
-	 * page.
-	 */
-	lg->pgdirs[0].gpgdir = setup_pagetables(lg, mem, initrd_size);
-	if (IS_ERR_VALUE(lg->pgdirs[0].gpgdir))
-		return lg->pgdirs[0].gpgdir;
-	lg->pgdirs[0].pgdir = (pgd_t *)get_zeroed_page(GFP_KERNEL);
-	if (!lg->pgdirs[0].pgdir)
+	/* lg (and lg->cpus[]) starts zeroed: this allocates a new pgdir */
+	cpu->cpu_pgd = new_pgdir(cpu, 0, &allocated);
+	if (!allocated)
 		return -ENOMEM;
 
-#ifdef CONFIG_X86_PAE
-	/* For PAE, we also create the initial mid-level. */
-	pgd = lg->pgdirs[0].pgdir;
-	pmd_table = (pmd_t *) get_zeroed_page(GFP_KERNEL);
-	if (!pmd_table)
-		return -ENOMEM;
-
-	set_pgd(pgd + SWITCHER_PGD_INDEX,
-		__pgd(__pa(pmd_table) | _PAGE_PRESENT));
-#endif
-
-	/* This is the current page table. */
-	lg->cpus[0].cpu_pgd = 0;
+	/* We start with a linear mapping until the initialize. */
+	cpu->linear_pages = true;
 	return 0;
 }
 
@@ -1095,10 +985,10 @@ void page_table_guest_data_init(struct lg_cpu *cpu)
 		 * of virtual addresses used by the Switcher.
 		 */
 		|| put_user(RESERVE_MEM * 1024 * 1024,
-			&cpu->lg->lguest_data->reserve_mem)
-		|| put_user(cpu->lg->pgdirs[0].gpgdir,
-			&cpu->lg->lguest_data->pgdir))
+			    &cpu->lg->lguest_data->reserve_mem)) {
 		kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
+		return;
+	}
 
 	/*
 	 * In flush_user_mappings() we loop from 0 to
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 9f1659c3d1f3..65af42f2d593 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -269,10 +269,10 @@ void lguest_arch_run_guest(struct lg_cpu *cpu)
 static int emulate_insn(struct lg_cpu *cpu)
 {
 	u8 insn;
-	unsigned int insnlen = 0, in = 0, shift = 0;
+	unsigned int insnlen = 0, in = 0, small_operand = 0;
 	/*
 	 * The eip contains the *virtual* address of the Guest's instruction:
-	 * guest_pa just subtracts the Guest's page_offset.
+	 * walk the Guest's page tables to find the "physical" address.
 	 */
 	unsigned long physaddr = guest_pa(cpu, cpu->regs->eip);
 
@@ -300,11 +300,10 @@ static int emulate_insn(struct lg_cpu *cpu)
 	}
 
 	/*
-	 * 0x66 is an "operand prefix".  It means it's using the upper 16 bits
-	 * of the eax register.
+	 * 0x66 is an "operand prefix".  It means a 16, not 32 bit in/out.
 	 */
 	if (insn == 0x66) {
-		shift = 16;
+		small_operand = 1;
 		/* The instruction is 1 byte so far, read the next byte. */
 		insnlen = 1;
 		insn = lgread(cpu, physaddr + insnlen, u8);
@@ -340,11 +339,14 @@ static int emulate_insn(struct lg_cpu *cpu)
 	 * traditionally means "there's nothing there".
 	 */
 	if (in) {
-		/* Lower bit tells is whether it's a 16 or 32 bit access */
-		if (insn & 0x1)
-			cpu->regs->eax = 0xFFFFFFFF;
-		else
-			cpu->regs->eax |= (0xFFFF << shift);
+		/* 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;
@@ -352,69 +354,6 @@ static int emulate_insn(struct lg_cpu *cpu)
 	return 1;
 }
 
-/*
- * Our hypercalls mechanism used to be based on direct software interrupts.
- * After Anthony's "Refactor hypercall infrastructure" kvm patch, we decided to
- * change over to using kvm hypercalls.
- *
- * KVM_HYPERCALL is actually a "vmcall" instruction, which generates an invalid
- * opcode fault (fault 6) on non-VT cpus, so the easiest solution seemed to be
- * an *emulation approach*: if the fault was really produced by an hypercall
- * (is_hypercall() does exactly this check), we can just call the corresponding
- * hypercall host implementation function.
- *
- * But these invalid opcode faults are notably slower than software interrupts.
- * So we implemented the *patching (or rewriting) approach*: every time we hit
- * the KVM_HYPERCALL opcode in Guest code, we patch it to the old "int 0x1f"
- * opcode, so next time the Guest calls this hypercall it will use the
- * faster trap mechanism.
- *
- * Matias even benchmarked it to convince you: this shows the average cycle
- * cost of a hypercall.  For each alternative solution mentioned above we've
- * made 5 runs of the benchmark:
- *
- * 1) direct software interrupt: 2915, 2789, 2764, 2721, 2898
- * 2) emulation technique: 3410, 3681, 3466, 3392, 3780
- * 3) patching (rewrite) technique: 2977, 2975, 2891, 2637, 2884
- *
- * One two-line function is worth a 20% hypercall speed boost!
- */
-static void rewrite_hypercall(struct lg_cpu *cpu)
-{
-	/*
-	 * This are the opcodes we use to patch the Guest.  The opcode for "int
-	 * $0x1f" is "0xcd 0x1f" but vmcall instruction is 3 bytes long, so we
-	 * complete the sequence with a NOP (0x90).
-	 */
-	u8 insn[3] = {0xcd, 0x1f, 0x90};
-
-	__lgwrite(cpu, guest_pa(cpu, cpu->regs->eip), insn, sizeof(insn));
-	/*
-	 * The above write might have caused a copy of that page to be made
-	 * (if it was read-only).  We need to make sure the Guest has
-	 * up-to-date pagetables.  As this doesn't happen often, we can just
-	 * drop them all.
-	 */
-	guest_pagetable_clear_all(cpu);
-}
-
-static bool is_hypercall(struct lg_cpu *cpu)
-{
-	u8 insn[3];
-
-	/*
-	 * This must be the Guest kernel trying to do something.
-	 * The bottom two bits of the CS segment register are the privilege
-	 * level.
-	 */
-	if ((cpu->regs->cs & 3) != GUEST_PL)
-		return false;
-
-	/* Is it a vmcall? */
-	__lgread(cpu, insn, guest_pa(cpu, cpu->regs->eip), sizeof(insn));
-	return insn[0] == 0x0f && insn[1] == 0x01 && insn[2] == 0xc1;
-}
-
 /*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
 void lguest_arch_handle_trap(struct lg_cpu *cpu)
 {
@@ -429,20 +368,6 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
 			if (emulate_insn(cpu))
 				return;
 		}
-		/*
-		 * If KVM is active, the vmcall instruction triggers a General
-		 * Protection Fault.  Normally it triggers an invalid opcode
-		 * fault (6):
-		 */
-	case 6:
-		/*
-		 * We need to check if ring == GUEST_PL and faulting
-		 * instruction == vmcall.
-		 */
-		if (is_hypercall(cpu)) {
-			rewrite_hypercall(cpu);
-			return;
-		}
 		break;
 	case 14: /* We've intercepted a Page Fault. */
 		/*
@@ -486,7 +411,7 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
 		 * 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
+		 * return to run the Guest again.
 		 */
 		cond_resched();
 		return;
@@ -536,7 +461,7 @@ void __init lguest_arch_host_init(void)
 	int i;
 
 	/*
-	 * Most of the i386/switcher.S doesn't care that it's been moved; on
+	 * 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.
 	 *
@@ -664,7 +589,7 @@ void __init lguest_arch_host_init(void)
 		clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
 	}
 	put_online_cpus();
-};
+}
 /*:*/
 
 void __exit lguest_arch_host_fini(void)
@@ -747,8 +672,6 @@ int lguest_arch_init_hypercalls(struct lg_cpu *cpu)
 /*:*/
 
 /*L:030
- * lguest_arch_setup_regs()
- *
  * Most of the Guest's registers are left alone: we used get_zeroed_page() to
  * allocate the structure, so they will be 0.
  */