Commit 17427e08 authored by Rusty Russell's avatar Rusty Russell
Browse files

lguest: extract shadow PTE walking / allocating. 



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: default avatarRusty Russell <rusty@rustcorp.com.au>
parent e1d12606

drivers/lguest/page_tables.c

+101 −69
Original line number Diff line number Diff line
@@ -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.

 *
@@ -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)
@@ -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)));

	}



#ifdef CONFIG_X86_PAE

	if (unlikely(cpu->linear_pages)) {

		/* Faking up a linear mapping. */

	/* This "mid-level" entry is only used for non-linear, PAE mode. */

	gpmd = __pmd(_PAGE_TABLE);

	} else {



#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;

	}



	/* 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)));

	}



	/*
@@ -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.
@@ -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);

}