[PATCH v13 48/85] KVM: x86/mmu: Don't mark unused faultin pages as accessed

Sean Christopherson
2024-10-10T18:26:34Z

When finishing guest page faults, don't mark pages as accessed if KVM
is resuming the guest _without_ installing a mapping, i.e. if the page
isn't being used. While it's possible that marking the page accessed
could avoid minor thrashing due to reclaiming a page that the guest is
about to access, it's far more likely that the gfn=>pfn mapping was
was invalidated, e.g. due a memslot change, or because the corresponding
VMA is being modified.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/mmu.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index f9b7e3a7370f..e14b84d2f55b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4386,7 +4386,9 @@ static void kvm_mmu_finish_page_fault(struct kvm_vcpu *vcpu,
* fault handler, and so KVM must (somewhat) speculatively mark the
* folio dirty if KVM could locklessly make the SPTE writable.
*/
- if (!fault->map_writable || r == RET_PF_RETRY)
+ if (r == RET_PF_RETRY)
+ kvm_release_page_unused(fault->refcounted_page);
+ else if (!fault->map_writable)
kvm_release_page_clean(fault->refcounted_page);
else
kvm_release_page_dirty(fault->refcounted_page);
--
2.47.0.rc1.288.g06298d1525-goog