[Lguest] lguest: mapping switcher would thwack fixmap
Rusty Russell
rusty at rustcorp.com.au
Wed Apr 17 12:08:15 EST 2013
Paul Bolle <pebolle at tiscali.nl> writes:
> On Thu, 2013-04-11 at 18:59 +0200, Paul Bolle wrote:
>> 1) And now running the lguest tools doesn't triple fault anymore. It
>> just panics the kernel. Progress!
>
> That must have been a very lucky run. I've tried half a dozen times to
> run the lguest tool with a serial line attached and every time all I got
> was a reboot. Nothing whatsoever was printed to the (serial) console.
OK, I did some cleanups along the way, but this seems to work for me.
You can either grab my pending-rebases branch from git.kernel.org (which
has all my pending patches in it), or apply the following mega-patch
which should be equivalent.
Please report back if this fixes the problem for you...
Thanks!
Rusty.
diff --git a/arch/x86/include/asm/lguest.h b/arch/x86/include/asm/lguest.h
index 0d97deb..e2d4a4a 100644
--- a/arch/x86/include/asm/lguest.h
+++ b/arch/x86/include/asm/lguest.h
@@ -11,18 +11,11 @@
#define GUEST_PL 1
-/* Every guest maps the core switcher code. */
-#define SHARED_SWITCHER_PAGES \
- DIV_ROUND_UP(end_switcher_text - start_switcher_text, PAGE_SIZE)
-/* Pages for switcher itself, then two pages per cpu */
-#define TOTAL_SWITCHER_PAGES (SHARED_SWITCHER_PAGES + 2 * nr_cpu_ids)
-
-/* We map at -4M (-2M for PAE) for ease of mapping (one PTE page). */
-#ifdef CONFIG_X86_PAE
-#define SWITCHER_ADDR 0xFFE00000
-#else
-#define SWITCHER_ADDR 0xFFC00000
-#endif
+/* Page for Switcher text itself, then two pages per cpu */
+#define TOTAL_SWITCHER_PAGES (1 + 2 * nr_cpu_ids)
+
+/* Where we map the Switcher, in both Host and Guest. */
+extern unsigned long switcher_addr;
/* Found in switcher.S */
extern unsigned long default_idt_entries[];
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index a5ebc00..0bf1e4e 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -20,9 +20,9 @@
#include <asm/asm-offsets.h>
#include "lg.h"
-
+unsigned long switcher_addr;
+struct page **lg_switcher_pages;
static struct vm_struct *switcher_vma;
-static struct page **switcher_page;
/* This One Big lock protects all inter-guest data structures. */
DEFINE_MUTEX(lguest_lock);
@@ -52,13 +52,21 @@ static __init int map_switcher(void)
* easy.
*/
+ /* We assume Switcher text fits into a single page. */
+ if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
+ printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
+ end_switcher_text - start_switcher_text);
+ return -EINVAL;
+ }
+
/*
* We allocate an array of struct page pointers. map_vm_area() wants
* this, rather than just an array of pages.
*/
- switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
- GFP_KERNEL);
- if (!switcher_page) {
+ lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
+ * TOTAL_SWITCHER_PAGES,
+ GFP_KERNEL);
+ if (!lg_switcher_pages) {
err = -ENOMEM;
goto out;
}
@@ -68,32 +76,29 @@ static __init int map_switcher(void)
* so we make sure they're zeroed.
*/
for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
- switcher_page[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
- if (!switcher_page[i]) {
+ lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
+ if (!lg_switcher_pages[i]) {
err = -ENOMEM;
goto free_some_pages;
}
}
/*
- * First we check that the Switcher won't overlap the fixmap area at
- * the top of memory. It's currently nowhere near, but it could have
- * very strange effects if it ever happened.
+ * We place the Switcher underneath the fixmap area, which is the
+ * highest virtual address we can get. This is important, since we
+ * tell the Guest it can't access this memory, so we want its ceiling
+ * as high as possible.
*/
- if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
- err = -ENOMEM;
- printk("lguest: mapping switcher would thwack fixmap\n");
- goto free_pages;
- }
+ switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE;
/*
- * Now we reserve the "virtual memory area" we want: 0xFFC00000
- * (SWITCHER_ADDR). We might not get it in theory, but in practice
- * it's worked so far. The end address needs +1 because __get_vm_area
- * allocates an extra guard page, so we need space for that.
+ * Now we reserve the "virtual memory area" we want. We might
+ * not get it in theory, but in practice it's worked so far.
+ * The end address needs +1 because __get_vm_area allocates an
+ * extra guard page, so we need space for that.
*/
switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
- VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
+ VM_ALLOC, switcher_addr, switcher_addr
+ (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
if (!switcher_vma) {
err = -ENOMEM;
@@ -103,12 +108,12 @@ static __init int map_switcher(void)
/*
* This code actually sets up the pages we've allocated to appear at
- * SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the
+ * switcher_addr. map_vm_area() takes the vma we allocated above, the
* kind of pages we're mapping (kernel pages), and a pointer to our
* array of struct pages. It increments that pointer, but we don't
* care.
*/
- pagep = switcher_page;
+ pagep = lg_switcher_pages;
err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
if (err) {
printk("lguest: map_vm_area failed: %i\n", err);
@@ -133,8 +138,8 @@ free_pages:
i = TOTAL_SWITCHER_PAGES;
free_some_pages:
for (--i; i >= 0; i--)
- __free_pages(switcher_page[i], 0);
- kfree(switcher_page);
+ __free_pages(lg_switcher_pages[i], 0);
+ kfree(lg_switcher_pages);
out:
return err;
}
@@ -149,8 +154,8 @@ static void unmap_switcher(void)
vunmap(switcher_vma->addr);
/* Now we just need to free the pages we copied the switcher into */
for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
- __free_pages(switcher_page[i], 0);
- kfree(switcher_page);
+ __free_pages(lg_switcher_pages[i], 0);
+ kfree(lg_switcher_pages);
}
/*H:032
@@ -323,15 +328,10 @@ static int __init init(void)
if (err)
goto out;
- /* Now we set up the pagetable implementation for the Guests. */
- err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
- if (err)
- goto unmap;
-
/* We might need to reserve an interrupt vector. */
err = init_interrupts();
if (err)
- goto free_pgtables;
+ goto unmap;
/* /dev/lguest needs to be registered. */
err = lguest_device_init();
@@ -346,8 +346,6 @@ static int __init init(void)
free_interrupts:
free_interrupts();
-free_pgtables:
- free_pagetables();
unmap:
unmap_switcher();
out:
@@ -359,7 +357,6 @@ static void __exit fini(void)
{
lguest_device_remove();
free_interrupts();
- free_pagetables();
unmap_switcher();
lguest_arch_host_fini();
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 295df06..2eef40b 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -14,11 +14,10 @@
#include <asm/lguest.h>
-void free_pagetables(void);
-int init_pagetables(struct page **switcher_page, unsigned int pages);
-
struct pgdir {
unsigned long gpgdir;
+ bool switcher_mapped;
+ int last_host_cpu;
pgd_t *pgdir;
};
@@ -124,6 +123,7 @@ bool lguest_address_ok(const struct lguest *lg,
unsigned long addr, unsigned long len);
void __lgread(struct lg_cpu *, void *, unsigned long, unsigned);
void __lgwrite(struct lg_cpu *, unsigned long, const void *, unsigned);
+extern struct page **lg_switcher_pages;
/*H:035
* Using memory-copy operations like that is usually inconvient, so we
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 3b62be16..b24add5 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -7,7 +7,7 @@
* converted Guest pages when running the Guest.
:*/
-/* Copyright (C) Rusty Russell IBM Corporation 2006.
+/* Copyright (C) Rusty Russell IBM Corporation 2013.
* GPL v2 and any later version */
#include <linux/mm.h>
#include <linux/gfp.h>
@@ -62,22 +62,11 @@
* will need the last pmd entry of the last pmd page.
*/
#ifdef CONFIG_X86_PAE
-#define SWITCHER_PMD_INDEX (PTRS_PER_PMD - 1)
-#define RESERVE_MEM 2U
#define CHECK_GPGD_MASK _PAGE_PRESENT
#else
-#define RESERVE_MEM 4U
#define CHECK_GPGD_MASK _PAGE_TABLE
#endif
-/*
- * We actually need a separate PTE page for each CPU. Remember that after the
- * Switcher code itself comes two pages for each CPU, and we don't want this
- * CPU's guest to see the pages of any other CPU.
- */
-static DEFINE_PER_CPU(pte_t *, switcher_pte_pages);
-#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
-
/*H:320
* The page table code is curly enough to need helper functions to keep it
* clear and clean. The kernel itself provides many of them; one advantage
@@ -95,13 +84,6 @@ static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
{
unsigned int index = pgd_index(vaddr);
-#ifndef CONFIG_X86_PAE
- /* We kill any Guest trying to touch the Switcher addresses. */
- if (index >= SWITCHER_PGD_INDEX) {
- kill_guest(cpu, "attempt to access switcher pages");
- index = 0;
- }
-#endif
/* Return a pointer index'th pgd entry for the i'th page table. */
return &cpu->lg->pgdirs[i].pgdir[index];
}
@@ -117,13 +99,6 @@ static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
unsigned int index = pmd_index(vaddr);
pmd_t *page;
- /* We kill any Guest trying to touch the Switcher addresses. */
- if (pgd_index(vaddr) == SWITCHER_PGD_INDEX &&
- index >= SWITCHER_PMD_INDEX) {
- kill_guest(cpu, "attempt to access switcher pages");
- index = 0;
- }
-
/* You should never call this if the PGD entry wasn't valid */
BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
@@ -275,122 +250,181 @@ static void release_pte(pte_t pte)
}
/*:*/
-static void check_gpte(struct lg_cpu *cpu, pte_t gpte)
+static bool check_gpte(struct lg_cpu *cpu, pte_t gpte)
{
if ((pte_flags(gpte) & _PAGE_PSE) ||
- pte_pfn(gpte) >= cpu->lg->pfn_limit)
+ pte_pfn(gpte) >= cpu->lg->pfn_limit) {
kill_guest(cpu, "bad page table entry");
+ return false;
+ }
+ return true;
}
-static void check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
+static bool check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
{
if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
- (pgd_pfn(gpgd) >= cpu->lg->pfn_limit))
+ (pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) {
kill_guest(cpu, "bad page directory entry");
+ return false;
+ }
+ return true;
}
#ifdef CONFIG_X86_PAE
-static void check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
+static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
{
if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
- (pmd_pfn(gpmd) >= cpu->lg->pfn_limit))
+ (pmd_pfn(gpmd) >= cpu->lg->pfn_limit)) {
kill_guest(cpu, "bad page middle directory entry");
+ return false;
+ }
+ return true;
}
#endif
-/*H:330
- * (i) Looking up a page table entry when the Guest faults.
- *
- * We saw this call in run_guest(): when we see a page fault in the Guest, we
- * come here. That's because we only set up the shadow page tables lazily as
- * they're needed, so we get page faults all the time and quietly fix them up
- * and return to the Guest without it knowing.
+/*H:331
+ * This is the core routine to walk the shadow page tables and find the page
+ * table entry for a specific address.
*
- * If we fixed up the fault (ie. we mapped the address), this routine returns
- * true. Otherwise, it was a real fault and we need to tell the Guest.
+ * If allocate is set, then we allocate any missing levels, setting the flags
+ * on the new page directory and mid-level directories using the arguments
+ * (which are copied from the Guest's page table entries).
*/
-bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
+static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
+ int pgd_flags, int pmd_flags)
{
- pgd_t gpgd;
pgd_t *spgd;
- unsigned long gpte_ptr;
- pte_t gpte;
- pte_t *spte;
-
/* Mid level for PAE. */
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
- pmd_t gpmd;
#endif
- /* First step: get the top-level Guest page table entry. */
- 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. */
+ /* Get top level entry. */
spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
/* No shadow entry: allocate a new shadow PTE page. */
- unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
+ unsigned long ptepage;
+
+ /* If they didn't want us to allocate anything, stop. */
+ if (!allocate)
+ return NULL;
+
+ ptepage = get_zeroed_page(GFP_KERNEL);
/*
* This is not really the Guest's fault, but killing it is
* simple for this corner case.
*/
if (!ptepage) {
kill_guest(cpu, "out of memory allocating pte page");
- return false;
+ return NULL;
}
- /* We check that the Guest pgd is OK. */
- check_gpgd(cpu, gpgd);
/*
* And we copy the flags to the shadow PGD entry. The page
* number in the shadow PGD is the page we just allocated.
*/
- set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags(gpgd)));
+ set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags));
}
+ /*
+ * Intel's Physical Address Extension actually uses three levels of
+ * page tables, so we need to look in the mid-level.
+ */
#ifdef CONFIG_X86_PAE
- 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. */
+ /* Now look at the mid-level shadow entry. */
spmd = spmd_addr(cpu, *spgd, vaddr);
if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
/* No shadow entry: allocate a new shadow PTE page. */
- unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
+ unsigned long ptepage;
+
+ /* If they didn't want us to allocate anything, stop. */
+ if (!allocate)
+ return NULL;
+
+ ptepage = get_zeroed_page(GFP_KERNEL);
/*
* This is not really the Guest's fault, but killing it is
* simple for this corner case.
*/
if (!ptepage) {
- kill_guest(cpu, "out of memory allocating pte page");
- return false;
+ kill_guest(cpu, "out of memory allocating pmd page");
+ return NULL;
}
- /* We check that the Guest pmd is OK. */
- check_gpmd(cpu, gpmd);
-
/*
* And we copy the flags to the shadow PMD entry. The page
* number in the shadow PMD is the page we just allocated.
*/
- set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags(gpmd)));
+ set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags));
+ }
+#endif
+
+ /* Get the pointer to the shadow PTE entry we're going to set. */
+ return spte_addr(cpu, *spgd, vaddr);
+}
+
+/*H:330
+ * (i) Looking up a page table entry when the Guest faults.
+ *
+ * We saw this call in run_guest(): when we see a page fault in the Guest, we
+ * come here. That's because we only set up the shadow page tables lazily as
+ * they're needed, so we get page faults all the time and quietly fix them up
+ * and return to the Guest without it knowing.
+ *
+ * If we fixed up the fault (ie. we mapped the address), this routine
+ * returns the page table entry. Otherwise, it returns NULL: a real
+ * fault and we need to tell the Guest.
+ *
+ * limit is usually set to the address of the first Switcher page: if a Guest
+ * hits that.
+ */
+bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
+{
+ unsigned long gpte_ptr;
+ pte_t gpte;
+ pte_t *spte;
+ pmd_t gpmd;
+ pgd_t gpgd;
+
+ /* We never demand page the Switcher, so trying is a mistake. */
+ if (vaddr >= switcher_addr)
+ return false;
+
+ /* First step: get the top-level Guest page table entry. */
+ 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;
+
+ /*
+ * This kills the Guest if it has weird flags or tries to
+ * refer to a "physical" address outside the bounds.
+ */
+ if (!check_gpgd(cpu, gpgd))
+ return false;
+ }
+
+ /* This "mid-level" entry is only used for non-linear, PAE mode. */
+ gpmd = __pmd(_PAGE_TABLE);
+
+#ifdef CONFIG_X86_PAE
+ if (likely(!cpu->linear_pages)) {
+ 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;
+
+ /*
+ * This kills the Guest if it has weird flags or tries to
+ * refer to a "physical" address outside the bounds.
+ */
+ if (!check_gpmd(cpu, gpmd))
+ return false;
}
/*
@@ -433,7 +467,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
* Check that the Guest PTE flags are OK, and the page number is below
* the pfn_limit (ie. not mapping the Launcher binary).
*/
- check_gpte(cpu, gpte);
+ if (!check_gpte(cpu, gpte))
+ return false;
/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
gpte = pte_mkyoung(gpte);
@@ -441,7 +476,9 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
gpte = pte_mkdirty(gpte);
/* Get the pointer to the shadow PTE entry we're going to set. */
- spte = spte_addr(cpu, *spgd, vaddr);
+ spte = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd));
+ if (!spte)
+ return false;
/*
* If there was a valid shadow PTE entry here before, we release it.
@@ -493,29 +530,23 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
*/
static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
{
- pgd_t *spgd;
+ pte_t *spte;
unsigned long flags;
-#ifdef CONFIG_X86_PAE
- pmd_t *spmd;
-#endif
- /* Look at the current top level entry: is it present? */
- spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
- if (!(pgd_flags(*spgd) & _PAGE_PRESENT))
+ /* You can't put your stack in the Switcher! */
+ if (vaddr >= switcher_addr)
return false;
-#ifdef CONFIG_X86_PAE
- spmd = spmd_addr(cpu, *spgd, vaddr);
- if (!(pmd_flags(*spmd) & _PAGE_PRESENT))
+ /* If there's no shadow PTE, it's not writable. */
+ spte = find_spte(cpu, vaddr, false, 0, 0);
+ if (!spte)
return false;
-#endif
/*
* Check the flags on the pte entry itself: it must be present and
* writable.
*/
- flags = pte_flags(*(spte_addr(cpu, *spgd, vaddr)));
-
+ flags = pte_flags(*spte);
return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
}
@@ -678,9 +709,6 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
int *blank_pgdir)
{
unsigned int next;
-#ifdef CONFIG_X86_PAE
- pmd_t *pmd_table;
-#endif
/*
* We pick one entry at random to throw out. Choosing the Least
@@ -695,29 +723,11 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
if (!cpu->lg->pgdirs[next].pgdir)
next = cpu->cpu_pgd;
else {
-#ifdef CONFIG_X86_PAE
/*
- * In PAE mode, allocate a pmd page and populate the
- * last pgd entry.
+ * This is a blank page, so there are no kernel
+ * mappings: caller must map the stack!
*/
- pmd_table = (pmd_t *)get_zeroed_page(GFP_KERNEL);
- if (!pmd_table) {
- free_page((long)cpu->lg->pgdirs[next].pgdir);
- set_pgd(cpu->lg->pgdirs[next].pgdir, __pgd(0));
- next = cpu->cpu_pgd;
- } else {
- set_pgd(cpu->lg->pgdirs[next].pgdir +
- SWITCHER_PGD_INDEX,
- __pgd(__pa(pmd_table) | _PAGE_PRESENT));
- /*
- * This is a blank page, so there are no kernel
- * mappings: caller must map the stack!
- */
- *blank_pgdir = 1;
- }
-#else
*blank_pgdir = 1;
-#endif
}
}
/* Record which Guest toplevel this shadows. */
@@ -725,9 +735,50 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
/* Release all the non-kernel mappings. */
flush_user_mappings(cpu->lg, next);
+ /* This hasn't run on any CPU at all. */
+ cpu->lg->pgdirs[next].last_host_cpu = -1;
+
return next;
}
+/*H:501
+ * We do need the Switcher code mapped at all times, so we allocate that
+ * part of the Guest page table here. We map the Switcher code immediately,
+ * but defer mapping of the guest register page and IDT/LDT etc page until
+ * just before we run the guest in map_switcher_in_guest().
+ *
+ * We *could* do this setup in map_switcher_in_guest(), but at that point
+ * we've interrupts disabled, and allocating pages like that is fraught: we
+ * can't sleep if we need to free up some memory.
+ */
+static bool allocate_switcher_mapping(struct lg_cpu *cpu)
+{
+ int i;
+
+ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
+ pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
+ CHECK_GPGD_MASK, _PAGE_TABLE);
+ if (!pte)
+ return false;
+
+ /*
+ * Map the switcher page if not already there. It might
+ * already be there because we call allocate_switcher_mapping()
+ * in guest_set_pgd() just in case it did discard our Switcher
+ * mapping, but it probably didn't.
+ */
+ if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) {
+ /* Get a reference to the Switcher page. */
+ get_page(lg_switcher_pages[0]);
+ /* Create a read-only, exectuable, kernel-style PTE */
+ set_pte(pte,
+ mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
+ }
+ }
+ cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true;
+ return true;
+}
+
/*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
@@ -738,28 +789,16 @@ static void release_all_pagetables(struct lguest *lg)
unsigned int i, j;
/* Every shadow pagetable this Guest has */
- for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
- if (lg->pgdirs[i].pgdir) {
-#ifdef CONFIG_X86_PAE
- pgd_t *spgd;
- pmd_t *pmdpage;
- unsigned int k;
-
- /* Get the last pmd page. */
- spgd = lg->pgdirs[i].pgdir + SWITCHER_PGD_INDEX;
- pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
-
- /*
- * And release the pmd entries of that pmd page,
- * except for the switcher pmd.
- */
- for (k = 0; k < SWITCHER_PMD_INDEX; k++)
- release_pmd(&pmdpage[k]);
-#endif
- /* Every PGD entry except the Switcher at the top */
- for (j = 0; j < SWITCHER_PGD_INDEX; j++)
- release_pgd(lg->pgdirs[i].pgdir + j);
- }
+ for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) {
+ if (!lg->pgdirs[i].pgdir)
+ continue;
+
+ /* Every PGD entry. */
+ for (j = 0; j < PTRS_PER_PGD; j++)
+ release_pgd(lg->pgdirs[i].pgdir + j);
+ lg->pgdirs[i].switcher_mapped = false;
+ lg->pgdirs[i].last_host_cpu = -1;
+ }
}
/*
@@ -773,6 +812,9 @@ void guest_pagetable_clear_all(struct lg_cpu *cpu)
release_all_pagetables(cpu->lg);
/* We need the Guest kernel stack mapped again. */
pin_stack_pages(cpu);
+ /* And we need Switcher allocated. */
+ if (!allocate_switcher_mapping(cpu))
+ kill_guest(cpu, "Cannot populate switcher mapping");
}
/*H:430
@@ -808,9 +850,17 @@ void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
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 it was completely blank, we map in the Guest kernel stack and
+ * the Switcher.
+ */
if (repin)
pin_stack_pages(cpu);
+
+ if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) {
+ if (!allocate_switcher_mapping(cpu))
+ kill_guest(cpu, "Cannot populate switcher mapping");
+ }
}
/*:*/
@@ -865,7 +915,8 @@ static void do_set_pte(struct lg_cpu *cpu, int idx,
* micro-benchmark.
*/
if (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
- check_gpte(cpu, gpte);
+ if (!check_gpte(cpu, gpte))
+ return;
set_pte(spte,
gpte_to_spte(cpu, gpte,
pte_flags(gpte) & _PAGE_DIRTY));
@@ -897,6 +948,12 @@ static void do_set_pte(struct lg_cpu *cpu, int idx,
void guest_set_pte(struct lg_cpu *cpu,
unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
{
+ /* We don't let you remap the Switcher; we need it to get back! */
+ if (vaddr >= switcher_addr) {
+ kill_guest(cpu, "attempt to set pte into Switcher pages");
+ return;
+ }
+
/*
* Kernel mappings must be changed on all top levels. Slow, but doesn't
* happen often.
@@ -933,14 +990,23 @@ void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
{
int pgdir;
- if (idx >= SWITCHER_PGD_INDEX)
+ if (idx > PTRS_PER_PGD) {
+ kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u",
+ idx, PTRS_PER_PGD);
return;
+ }
/* If they're talking about a page table we have a shadow for... */
pgdir = find_pgdir(lg, gpgdir);
- if (pgdir < ARRAY_SIZE(lg->pgdirs))
+ if (pgdir < ARRAY_SIZE(lg->pgdirs)) {
/* ... throw it away. */
release_pgd(lg->pgdirs[pgdir].pgdir + idx);
+ /* That might have been the Switcher mapping, remap it. */
+ if (!allocate_switcher_mapping(&lg->cpus[0])) {
+ kill_guest(&lg->cpus[0],
+ "Cannot populate switcher mapping");
+ }
+ }
}
#ifdef CONFIG_X86_PAE
@@ -958,6 +1024,9 @@ void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
* 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.
+ *
+ * We do need the Switcher to be mapped at all times, so we allocate that
+ * part of the Guest page table here.
*/
int init_guest_pagetable(struct lguest *lg)
{
@@ -971,21 +1040,34 @@ int init_guest_pagetable(struct lguest *lg)
/* We start with a linear mapping until the initialize. */
cpu->linear_pages = true;
+
+ /* Allocate the page tables for the Switcher. */
+ if (!allocate_switcher_mapping(cpu)) {
+ release_all_pagetables(lg);
+ return -ENOMEM;
+ }
+
return 0;
}
/*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
void page_table_guest_data_init(struct lg_cpu *cpu)
{
+ /*
+ * We tell the Guest that it can't use the virtual addresses
+ * used by the Switcher. This trick is equivalent to 4GB -
+ * switcher_addr.
+ */
+ u32 top = ~switcher_addr + 1;
+
/* We get the kernel address: above this is all kernel memory. */
if (get_user(cpu->lg->kernel_address,
- &cpu->lg->lguest_data->kernel_address)
+ &cpu->lg->lguest_data->kernel_address)
/*
- * We tell the Guest that it can't use the top 2 or 4 MB
- * of virtual addresses used by the Switcher.
+ * We tell the Guest that it can't use the top virtual
+ * addresses (used by the Switcher).
*/
- || put_user(RESERVE_MEM * 1024 * 1024,
- &cpu->lg->lguest_data->reserve_mem)) {
+ || put_user(top, &cpu->lg->lguest_data->reserve_mem)) {
kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
return;
}
@@ -995,12 +1077,7 @@ void page_table_guest_data_init(struct lg_cpu *cpu)
* "pgd_index(lg->kernel_address)". This assumes it won't hit the
* Switcher mappings, so check that now.
*/
-#ifdef CONFIG_X86_PAE
- if (pgd_index(cpu->lg->kernel_address) == SWITCHER_PGD_INDEX &&
- pmd_index(cpu->lg->kernel_address) == SWITCHER_PMD_INDEX)
-#else
- if (pgd_index(cpu->lg->kernel_address) >= SWITCHER_PGD_INDEX)
-#endif
+ if (cpu->lg->kernel_address >= switcher_addr)
kill_guest(cpu, "bad kernel address %#lx",
cpu->lg->kernel_address);
}
@@ -1017,102 +1094,96 @@ void free_guest_pagetable(struct lguest *lg)
free_page((long)lg->pgdirs[i].pgdir);
}
-/*H:480
- * (vi) Mapping the Switcher when the Guest is about to run.
- *
- * The Switcher and the two pages for this CPU need to be visible in the
- * Guest (and not the pages for other CPUs). We have the appropriate PTE pages
- * for each CPU already set up, we just need to hook them in now we know which
- * Guest is about to run on this CPU.
+/*H:481
+ * This clears the Switcher mappings for cpu #i.
*/
-void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
+static void remove_switcher_percpu_map(struct lg_cpu *cpu, unsigned int i)
{
- pte_t *switcher_pte_page = __this_cpu_read(switcher_pte_pages);
- pte_t regs_pte;
+ unsigned long base = switcher_addr + PAGE_SIZE + i * PAGE_SIZE*2;
+ pte_t *pte;
-#ifdef CONFIG_X86_PAE
- pmd_t switcher_pmd;
- pmd_t *pmd_table;
-
- switcher_pmd = pfn_pmd(__pa(switcher_pte_page) >> PAGE_SHIFT,
- PAGE_KERNEL_EXEC);
-
- /* Figure out where the pmd page is, by reading the PGD, and converting
- * it to a virtual address. */
- pmd_table = __va(pgd_pfn(cpu->lg->
- pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX])
- << PAGE_SHIFT);
- /* Now write it into the shadow page table. */
- set_pmd(&pmd_table[SWITCHER_PMD_INDEX], switcher_pmd);
-#else
- pgd_t switcher_pgd;
-
- /*
- * Make the last PGD entry for this Guest point to the Switcher's PTE
- * page for this CPU (with appropriate flags).
- */
- switcher_pgd = __pgd(__pa(switcher_pte_page) | __PAGE_KERNEL_EXEC);
-
- cpu->lg->pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
-
-#endif
- /*
- * We also change the Switcher PTE page. When we're running the Guest,
- * we want the Guest's "regs" page to appear where the first Switcher
- * page for this CPU is. This is an optimization: when the Switcher
- * saves the Guest registers, it saves them into the first page of this
- * CPU's "struct lguest_pages": if we make sure the Guest's register
- * page is already mapped there, we don't have to copy them out
- * again.
- */
- regs_pte = pfn_pte(__pa(cpu->regs_page) >> PAGE_SHIFT, PAGE_KERNEL);
- set_pte(&switcher_pte_page[pte_index((unsigned long)pages)], regs_pte);
-}
-/*:*/
-
-static void free_switcher_pte_pages(void)
-{
- unsigned int i;
+ /* Clear the mappings for both pages. */
+ pte = find_spte(cpu, base, false, 0, 0);
+ release_pte(*pte);
+ set_pte(pte, __pte(0));
- for_each_possible_cpu(i)
- free_page((long)switcher_pte_page(i));
+ pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
+ release_pte(*pte);
+ set_pte(pte, __pte(0));
}
-/*H:520
- * Setting up the Switcher PTE page for given CPU is fairly easy, given
- * the CPU number and the "struct page"s for the Switcher code itself.
+/*H:480
+ * (vi) Mapping the Switcher when the Guest is about to run.
+ *
+ * The Switcher and the two pages for this CPU need to be visible in the Guest
+ * (and not the pages for other CPUs).
*
- * Currently the Switcher is less than a page long, so "pages" is always 1.
+ * The pages for the pagetables have all been allocated before: we just need
+ * to make sure the actual PTEs are up-to-date for the CPU we're about to run
+ * on.
*/
-static __init void populate_switcher_pte_page(unsigned int cpu,
- struct page *switcher_page[],
- unsigned int pages)
+void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
{
- unsigned int i;
- pte_t *pte = switcher_pte_page(cpu);
+ unsigned long base;
+ struct page *percpu_switcher_page, *regs_page;
+ pte_t *pte;
+ struct pgdir *pgdir = &cpu->lg->pgdirs[cpu->cpu_pgd];
+
+ /* Switcher page should always be mapped by now! */
+ BUG_ON(!pgdir->switcher_mapped);
+
+ /*
+ * Remember that we have two pages for each Host CPU, so we can run a
+ * Guest on each CPU without them interfering. We need to make sure
+ * those pages are mapped correctly in the Guest, but since we usually
+ * run on the same CPU, we cache that, and only update the mappings
+ * when we move.
+ */
+ if (pgdir->last_host_cpu == raw_smp_processor_id())
+ return;
- /* The first entries are easy: they map the Switcher code. */
- for (i = 0; i < pages; i++) {
- set_pte(&pte[i], mk_pte(switcher_page[i],
- __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
+ /* -1 means unknown so we remove everything. */
+ if (pgdir->last_host_cpu == -1) {
+ unsigned int i;
+ for_each_possible_cpu(i)
+ remove_switcher_percpu_map(cpu, i);
+ } else {
+ /* We know exactly what CPU mapping to remove. */
+ remove_switcher_percpu_map(cpu, pgdir->last_host_cpu);
}
- /* The only other thing we map is this CPU's pair of pages. */
- i = pages + cpu*2;
-
- /* First page (Guest registers) is writable from the Guest */
- set_pte(&pte[i], pfn_pte(page_to_pfn(switcher_page[i]),
- __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW)));
+ /*
+ * When we're running the Guest, we want the Guest's "regs" page to
+ * appear where the first Switcher page for this CPU is. This is an
+ * optimization: when the Switcher saves the Guest registers, it saves
+ * them into the first page of this CPU's "struct lguest_pages": if we
+ * make sure the Guest's register page is already mapped there, we
+ * don't have to copy them out again.
+ */
+ /* Find the shadow PTE for this regs page. */
+ base = switcher_addr + PAGE_SIZE
+ + raw_smp_processor_id() * sizeof(struct lguest_pages);
+ pte = find_spte(cpu, base, false, 0, 0);
+ regs_page = pfn_to_page(__pa(cpu->regs_page) >> PAGE_SHIFT);
+ get_page(regs_page);
+ set_pte(pte, mk_pte(regs_page, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL)));
/*
- * The second page contains the "struct lguest_ro_state", and is
- * read-only.
+ * We map the second page of the struct lguest_pages read-only in
+ * the Guest: the IDT, GDT and other things it's not supposed to
+ * change.
*/
- set_pte(&pte[i+1], pfn_pte(page_to_pfn(switcher_page[i+1]),
- __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
+ pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
+ percpu_switcher_page
+ = lg_switcher_pages[1 + raw_smp_processor_id()*2 + 1];
+ get_page(percpu_switcher_page);
+ set_pte(pte, mk_pte(percpu_switcher_page,
+ __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL)));
+
+ pgdir->last_host_cpu = raw_smp_processor_id();
}
-/*
+/*H:490
* We've made it through the page table code. Perhaps our tired brains are
* still processing the details, or perhaps we're simply glad it's over.
*
@@ -1124,29 +1195,3 @@ static __init void populate_switcher_pte_page(unsigned int cpu,
*
* There is just one file remaining in the Host.
*/
-
-/*H:510
- * At boot or module load time, init_pagetables() allocates and populates
- * the Switcher PTE page for each CPU.
- */
-__init int init_pagetables(struct page **switcher_page, unsigned int pages)
-{
- unsigned int i;
-
- for_each_possible_cpu(i) {
- switcher_pte_page(i) = (pte_t *)get_zeroed_page(GFP_KERNEL);
- if (!switcher_pte_page(i)) {
- free_switcher_pte_pages();
- return -ENOMEM;
- }
- populate_switcher_pte_page(i, switcher_page, pages);
- }
- return 0;
-}
-/*:*/
-
-/* Cleaning up simply involves freeing the PTE page for each CPU. */
-void free_pagetables(void)
-{
- free_switcher_pte_pages();
-}
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 4af12e1..f0a3347 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -59,14 +59,13 @@ static struct {
/* 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;
+ return switcher_addr - (unsigned long)start_switcher_text;
}
-/* This cpu's struct lguest_pages. */
+/* This cpu's struct lguest_pages (after the Switcher text page) */
static struct lguest_pages *lguest_pages(unsigned int cpu)
{
- return &(((struct lguest_pages *)
- (SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
+ return &(((struct lguest_pages *)(switcher_addr + PAGE_SIZE))[cpu]);
}
static DEFINE_PER_CPU(struct lg_cpu *, lg_last_cpu);
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