Delete a shadow page from the invalidation list instead of throwing it
back on the list of active pages when it's a root shadow page with
active users. Invalid active root pages will be explicitly freed by
mmu_free_root_page() when the root_count hits zero, i.e. they don't need
to be put on the active list to avoid leakage.
Use sp->role.invalid to detect that a shadow page has already been
zapped, i.e. is not on a list.
WARN if an invalid page is encountered when zapping pages, as it should
now be impossible.
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 28 ++++++++++++++++++++--------
1 file changed, 20 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3dd0af7e7515..8e7df4ed4b55 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2757,10 +2757,23 @@ static bool __kvm_mmu_prepare_zap_page(struct kvm *kvm,
if (!sp->root_count) {
/* Count self */
(*nr_zapped)++;
- list_move(&sp->link, invalid_list);
+
+ /*
+ * Already invalid pages (previously active roots) are not on
+ * the active page list. See list_del() in the "else" case of
+ * !sp->root_count.
+ */
+ if (sp->role.invalid)
+ list_add(&sp->link, invalid_list);
+ else
+ list_move(&sp->link, invalid_list);
kvm_mod_used_mmu_pages(kvm, -1);
} else {
- list_move(&sp->link, &kvm->arch.active_mmu_pages);
+ /*
+ * Remove the active root from the active page list, the root
+ * will be explicitly freed when the root_count hits zero.
+ */
+ list_del(&sp->link);
/*
* Obsolete pages cannot be used on any vCPUs, see the comment
@@ -5727,12 +5740,11 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm)
break;
/*
- * Skip invalid pages with a non-zero root count, zapping pages
- * with a non-zero root count will never succeed, i.e. the page
- * will get thrown back on active_mmu_pages and we'll get stuck
- * in an infinite loop.
+ * Invalid pages should never land back on the list of active
+ * pages. Skip the bogus page, otherwise we'll get stuck in an
+ * infinite loop if the page gets put back on the list (again).
*/
- if (sp->role.invalid && sp->root_count)
+ if (WARN_ON(sp->role.invalid))
continue;
/*
@@ -6010,7 +6022,7 @@ void kvm_mmu_zap_all(struct kvm *kvm)
spin_lock(&kvm->mmu_lock);
restart:
list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
- if (sp->role.invalid && sp->root_count)
+ if (WARN_ON(sp->role.invalid))
continue;
if (__kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list, &ign))
goto restart;
--
2.26.0
