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Commit d7824fff authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: MMU: Avoid calling gfn_to_page() in mmu_set_spte() 



Since gfn_to_page() is a sleeping function, and we want to make the core mmu
spinlocked, we need to pass the page from the walker context (which can sleep)
to the shadow context (which cannot).

[marcelo: avoid recursive locking of mmap_sem]

Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 7ec54588

arch/x86/kvm/mmu.c

+50 −5
Original line number Diff line number Diff line
@@ -890,11 +890,10 @@ struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva) 
static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,

			 unsigned pt_access, unsigned pte_access,

			 int user_fault, int write_fault, int dirty,

			 int *ptwrite, gfn_t gfn)

			 int *ptwrite, gfn_t gfn, struct page *page)

{

	u64 spte;

	int was_rmapped = is_rmap_pte(*shadow_pte);

	struct page *page;



	pgprintk("%s: spte %llx access %x write_fault %d"

		 " user_fault %d gfn %lx\n",
@@ -912,8 +911,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte, 
	if (!(pte_access & ACC_EXEC_MASK))

		spte |= PT64_NX_MASK;



	page = gfn_to_page(vcpu->kvm, gfn);



	spte |= PT_PRESENT_MASK;

	if (pte_access & ACC_USER_MASK)

		spte |= PT_USER_MASK;
@@ -979,6 +976,11 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn) 
	int level = PT32E_ROOT_LEVEL;

	hpa_t table_addr = vcpu->arch.mmu.root_hpa;

	int pt_write = 0;

	struct page *page;



	down_read(&current->mm->mmap_sem);

	page = gfn_to_page(vcpu->kvm, gfn);

	up_read(&current->mm->mmap_sem);



	for (; ; level--) {

		u32 index = PT64_INDEX(v, level);
@@ -989,7 +991,7 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn) 


		if (level == 1) {

			mmu_set_spte(vcpu, &table[index], ACC_ALL, ACC_ALL,

				     0, write, 1, &pt_write, gfn);

				     0, write, 1, &pt_write, gfn, page);

			return pt_write || is_io_pte(table[index]);

		}
@@ -1005,6 +1007,7 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn) 
						     NULL);

			if (!new_table) {

				pgprintk("nonpaging_map: ENOMEM\n");

				kvm_release_page_clean(page);

				return -ENOMEM;

			}
@@ -1347,6 +1350,43 @@ static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu) 
	return !!(spte && (*spte & PT_ACCESSED_MASK));

}



static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,

					  const u8 *new, int bytes)

{

	gfn_t gfn;

	int r;

	u64 gpte = 0;



	if (bytes != 4 && bytes != 8)

		return;



	/*

	 * Assume that the pte write on a page table of the same type

	 * as the current vcpu paging mode.  This is nearly always true

	 * (might be false while changing modes).  Note it is verified later

	 * by update_pte().

	 */

	if (is_pae(vcpu)) {

		/* Handle a 32-bit guest writing two halves of a 64-bit gpte */

		if ((bytes == 4) && (gpa % 4 == 0)) {

			r = kvm_read_guest(vcpu->kvm, gpa & ~(u64)7, &gpte, 8);

			if (r)

				return;

			memcpy((void *)&gpte + (gpa % 8), new, 4);

		} else if ((bytes == 8) && (gpa % 8 == 0)) {

			memcpy((void *)&gpte, new, 8);

		}

	} else {

		if ((bytes == 4) && (gpa % 4 == 0))

			memcpy((void *)&gpte, new, 4);

	}

	if (!is_present_pte(gpte))

		return;

	gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;

	vcpu->arch.update_pte.gfn = gfn;

	vcpu->arch.update_pte.page = gfn_to_page(vcpu->kvm, gfn);

}



void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,

		       const u8 *new, int bytes)

{
@@ -1367,6 +1407,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, 
	int npte;



	pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);

	mmu_guess_page_from_pte_write(vcpu, gpa, new, bytes);

	mutex_lock(&vcpu->kvm->lock);

	++vcpu->kvm->stat.mmu_pte_write;

	kvm_mmu_audit(vcpu, "pre pte write");
@@ -1437,6 +1478,10 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, 
	}

	kvm_mmu_audit(vcpu, "post pte write");

	mutex_unlock(&vcpu->kvm->lock);

	if (vcpu->arch.update_pte.page) {

		kvm_release_page_clean(vcpu->arch.update_pte.page);

		vcpu->arch.update_pte.page = NULL;

	}

}



int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)

arch/x86/kvm/paging_tmpl.h

+18 −5
Original line number Diff line number Diff line
@@ -245,6 +245,7 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page, 
{

	pt_element_t gpte;

	unsigned pte_access;

	struct page *npage;



	gpte = *(const pt_element_t *)pte;

	if (~gpte & (PT_PRESENT_MASK | PT_ACCESSED_MASK)) {
@@ -256,8 +257,14 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page, 
		return;

	pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);

	pte_access = page->role.access & FNAME(gpte_access)(vcpu, gpte);

	if (gpte_to_gfn(gpte) != vcpu->arch.update_pte.gfn)

		return;

	npage = vcpu->arch.update_pte.page;

	if (!npage)

		return;

	get_page(npage);

	mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,

		     gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte));

		     gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte), npage);

}



/*
@@ -265,7 +272,8 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page, 
 */

static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,

			 struct guest_walker *walker,

			 int user_fault, int write_fault, int *ptwrite)

			 int user_fault, int write_fault, int *ptwrite,

			 struct page *page)

{

	hpa_t shadow_addr;

	int level;
@@ -321,9 +329,11 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, 
			r = kvm_read_guest_atomic(vcpu->kvm,

						  walker->pte_gpa[level - 2],

						  &curr_pte, sizeof(curr_pte));

			if (r || curr_pte != walker->ptes[level - 2])

			if (r || curr_pte != walker->ptes[level - 2]) {

				kvm_release_page_clean(page);

				return NULL;

			}

		}

		shadow_addr = __pa(shadow_page->spt);

		shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK

			| PT_WRITABLE_MASK | PT_USER_MASK;
@@ -333,7 +343,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, 
	mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,

		     user_fault, write_fault,

		     walker->ptes[walker->level-1] & PT_DIRTY_MASK,

		     ptwrite, walker->gfn);

		     ptwrite, walker->gfn, page);



	return shadow_ent;

}
@@ -362,6 +372,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, 
	u64 *shadow_pte;

	int write_pt = 0;

	int r;

	struct page *page;



	pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);

	kvm_mmu_audit(vcpu, "pre page fault");
@@ -388,9 +399,11 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, 
		return 0;

	}



	page = gfn_to_page(vcpu->kvm, walker.gfn);



	mutex_lock(&vcpu->kvm->lock);

	shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,

				  &write_pt);

				  &write_pt, page);

	pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __FUNCTION__,

		 shadow_pte, *shadow_pte, write_pt);

include/asm-x86/kvm_host.h

+5 −0
Original line number Diff line number Diff line
@@ -224,6 +224,11 @@ struct kvm_vcpu_arch { 
	int   last_pt_write_count;

	u64  *last_pte_updated;



	struct {

		gfn_t gfn;          /* presumed gfn during guest pte update */

		struct page *page;  /* page corresponding to that gfn */

	} update_pte;



	struct i387_fxsave_struct host_fx_image;

	struct i387_fxsave_struct guest_fx_image;