[PATCH v6 4/4] KVM: mmu: remove over-aggressive warnings

David Stevens
2023-03-30T08:58:55Z

From: David Stevens <stevensd@chromium.org>

Remove two warnings that require ref counts for pages to be non-zero, as
mapped pfns from follow_pfn may not have an initialized ref count.

Signed-off-by: David Stevens <stevensd@chromium.org>
---
arch/x86/kvm/mmu/mmu.c | 10 ----------
virt/kvm/kvm_main.c | 5 ++---
2 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 86b74e7bccfa..46b3d6c0ff27 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -555,7 +555,6 @@ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
kvm_pfn_t pfn;
u64 old_spte = *sptep;
int level = sptep_to_sp(sptep)->role.level;
- struct page *page;

if (!is_shadow_present_pte(old_spte) ||
!spte_has_volatile_bits(old_spte))
@@ -570,15 +569,6 @@ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)

pfn = spte_to_pfn(old_spte);

- /*
- * KVM doesn't hold a reference to any pages mapped into the guest, and
- * instead uses the mmu_notifier to ensure that KVM unmaps any pages
- * before they are reclaimed. Sanity check that, if the pfn is backed
- * by a refcounted page, the refcount is elevated.
- */
- page = kvm_pfn_to_refcounted_page(pfn);
- WARN_ON(page && !page_count(page));
-
if (is_accessed_spte(old_spte))
kvm_set_pfn_accessed(pfn);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 007dd984eeea..a80070cb04d7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -165,10 +165,9 @@ bool kvm_is_zone_device_page(struct page *page)
/*
* The metadata used by is_zone_device_page() to determine whether or
* not a page is ZONE_DEVICE is guaranteed to be valid if and only if
- * the device has been pinned, e.g. by get_user_pages(). WARN if the
- * page_count() is zero to help detect bad usage of this helper.
+ * the device has been pinned, e.g. by get_user_pages().
*/
- if (WARN_ON_ONCE(!page_count(page)))
+ if (!page_count(page))
return false;

return is_zone_device_page(page);
--
2.40.0.348.gf938b09366-goog