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lguest: extract shadow PTE walking / allocating.
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We want a separate find_pte() function so we can call it for populating the
switcher PTE entries.

We can also use it in page_writable().

Signed-off-by: Rusty Russell <[email protected]>
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@rustyrussell
rustyrussell committed Apr 22, 2013
1 parent e1d1260 commit 17427e0
Showing 1 changed file with 101 additions and 69 deletions.
170 changes: 101 additions & 69 deletions drivers/lguest/page_tables.c
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Original file line number Diff line number Diff line change
Expand Up @@ -291,6 +291,88 @@ static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
}
#endif

/*H:331
* This is the core routine to walk the shadow page tables and find the page
* table entry for a specific address.
*
* 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).
*/
static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
int pgd_flags, int pmd_flags)
{
pgd_t *spgd;
/* Mid level for PAE. */
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
#endif

/* 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;

/* 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 NULL;
}
/*
* 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));
}

/*
* 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
/* 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;

/* 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 pmd page");
return NULL;
}

/*
* 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));
}
#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.
*
Expand All @@ -304,17 +386,11 @@ static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
*/
bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
{
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
pgd_t gpgd;

/* We never demand page the Switcher, so trying is a mistake. */
if (vaddr >= switcher_addr)
Expand All @@ -329,67 +405,31 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
/* 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);
if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
/* No shadow entry: allocate a new shadow PTE page. */
unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
/*
* This is not really the Guest's fault, but killing it is
* simple for this corner case.
/*
* This kills the Guest if it has weird flags or tries to
* refer to a "physical" address outside the bounds.
*/
if (!ptepage) {
kill_guest(cpu, "out of memory allocating pte page");
return false;
}
/* We check that the Guest pgd is OK. */
if (!check_gpgd(cpu, gpgd))
return false;
/*
* 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)));
}

/* This "mid-level" entry is only used for non-linear, PAE mode. */
gpmd = __pmd(_PAGE_TABLE);

#ifdef CONFIG_X86_PAE
if (unlikely(cpu->linear_pages)) {
/* Faking up a linear mapping. */
gpmd = __pmd(_PAGE_TABLE);
} else {
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;
}

/* Now look at the matching 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);

/*
* This is not really the Guest's fault, but killing it is
* simple for this corner case.
/*
* This kills the Guest if it has weird flags or tries to
* refer to a "physical" address outside the bounds.
*/
if (!ptepage) {
kill_guest(cpu, "out of memory allocating pte page");
return false;
}

/* We check that the Guest pmd is OK. */
if (!check_gpmd(cpu, gpmd))
return false;

/*
* 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)));
}

/*
Expand Down Expand Up @@ -441,7 +481,9 @@ 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.
Expand Down Expand Up @@ -493,33 +535,23 @@ 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

/* You can't put your stack in the Switcher! */
if (vaddr >= switcher_addr)
return false;

/* Look at the current top level entry: is it present? */
spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
if (!(pgd_flags(*spgd) & _PAGE_PRESENT))
/* If there's no shadow PTE, it's not writable. */
spte = find_spte(cpu, vaddr, false, 0, 0);
if (!spte)
return false;

#ifdef CONFIG_X86_PAE
spmd = spmd_addr(cpu, *spgd, vaddr);
if (!(pmd_flags(*spmd) & _PAGE_PRESENT))
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);
}

Expand Down

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