[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: Avi Kivity <avi@qumranet.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 0e44aca..f163214 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -550,8 +550,13 @@
*parent_pte = 0;
}
kvm_mmu_page_unlink_children(vcpu, page);
- hlist_del(&page->hash_link);
- kvm_mmu_free_page(vcpu, page->page_hpa);
+ 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 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 @@
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 @@
{
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 @@
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 @@
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);