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Commit 3bb65a22 authored by Avi Kivity's avatar Avi Kivity Committed by Linus Torvalds
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[PATCH] KVM: MMU: Never free a shadow page actively serving as a root 



We always need cr3 to point to something valid, so if we detect that we're
freeing a root page, simply push it back to the top of the active list.

Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 86a5ba02

drivers/kvm/kvm.h

+1 −0
Original line number Diff line number Diff line
@@ -134,6 +134,7 @@ struct kvm_mmu_page { 
				    */

	int global;              /* Set if all ptes in this page are global */

	int multimapped;         /* More than one parent_pte? */

	int root_count;          /* Currently serving as active root */

	union {

		u64 *parent_pte;               /* !multimapped */

		struct hlist_head parent_ptes; /* multimapped, kvm_pte_chain */

drivers/kvm/mmu.c

+18 −2
Original line number Diff line number Diff line
@@ -550,8 +550,13 @@ static void kvm_mmu_zap_page(struct kvm_vcpu *vcpu, 
		*parent_pte = 0;

	}

	kvm_mmu_page_unlink_children(vcpu, page);

	if (!page->root_count) {

		hlist_del(&page->hash_link);

		kvm_mmu_free_page(vcpu, page->page_hpa);

	} else {

		list_del(&page->link);

		list_add(&page->link, &vcpu->kvm->active_mmu_pages);

	}

}



static int kvm_mmu_unprotect_page(struct kvm_vcpu *vcpu, gfn_t gfn)
@@ -667,12 +672,15 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p) 
static void mmu_free_roots(struct kvm_vcpu *vcpu)

{

	int i;

	struct kvm_mmu_page *page;



#ifdef CONFIG_X86_64

	if (vcpu->mmu.shadow_root_level == PT64_ROOT_LEVEL) {

		hpa_t root = vcpu->mmu.root_hpa;



		ASSERT(VALID_PAGE(root));

		page = page_header(root);

		--page->root_count;

		vcpu->mmu.root_hpa = INVALID_PAGE;

		return;

	}
@@ -682,6 +690,8 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu) 


		ASSERT(VALID_PAGE(root));

		root &= PT64_BASE_ADDR_MASK;

		page = page_header(root);

		--page->root_count;

		vcpu->mmu.pae_root[i] = INVALID_PAGE;

	}

	vcpu->mmu.root_hpa = INVALID_PAGE;
@@ -691,6 +701,8 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu) 
{

	int i;

	gfn_t root_gfn;

	struct kvm_mmu_page *page;



	root_gfn = vcpu->cr3 >> PAGE_SHIFT;



#ifdef CONFIG_X86_64
@@ -700,6 +712,8 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu) 
		ASSERT(!VALID_PAGE(root));

		root = kvm_mmu_get_page(vcpu, root_gfn, 0,

					PT64_ROOT_LEVEL, 0, NULL)->page_hpa;

		page = page_header(root);

		++page->root_count;

		vcpu->mmu.root_hpa = root;

		return;

	}
@@ -715,6 +729,8 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu) 
		root = kvm_mmu_get_page(vcpu, root_gfn, i << 30,

					PT32_ROOT_LEVEL, !is_paging(vcpu),

					NULL)->page_hpa;

		page = page_header(root);

		++page->root_count;

		vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;

	}

	vcpu->mmu.root_hpa = __pa(vcpu->mmu.pae_root);