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KVM: x86/mmu: Don't put invalid SPs back on the list of active pages

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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@intel.com>
Message-Id: <20200623193542.7554-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-06-23 12:35:39 -07:00 committed by Paolo Bonzini
parent fb58a9c345
commit f95eec9bed
1 changed files with 20 additions and 8 deletions
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28
arch/x86/kvm/mmu/mmu.c
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@ -2748,10 +2748,23 @@ 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
@ -5718,12 +5731,11 @@ 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;
/*
@ -6001,7 +6013,7 @@ 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;