KVM: MIPS: Mark "struct page" pfns accessed only in "slow" page fault path

Mark pages accessed only in the slow page fault path in order to remove
an unnecessary user of kvm_pfn_to_refcounted_page().  Marking pages
accessed in the primary MMU during KVM page fault handling isn't harmful,
but it's largely pointless and likely a waste of a cycles since the
primary MMU will call into KVM via mmu_notifiers when aging pages.  I.e.
KVM participates in a "pull" model, so there's no need to also "push"
updates.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-71-seanjc@google.com>

diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c
index 4da9ce4eb54dbe5c433c43cec052d95c57f87748..f1e4b618ec6d5b6d9beb2240659ef30bd0c60d29 100644 (file)
--- a/arch/mips/kvm/mmu.c
+++ b/arch/mips/kvm/mmu.c
@@ -484,8 +484,6 @@ static int _kvm_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
        struct kvm *kvm = vcpu->kvm;
        gfn_t gfn = gpa >> PAGE_SHIFT;
        pte_t *ptep;
-       kvm_pfn_t pfn = 0;      /* silence bogus GCC warning */
-       bool pfn_valid = false;
        int ret = 0;
 
        spin_lock(&kvm->mmu_lock);
@@ -498,12 +496,9 @@ static int _kvm_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
        }
 
        /* Track access to pages marked old */
-       if (!pte_young(*ptep)) {
+       if (!pte_young(*ptep))
                set_pte(ptep, pte_mkyoung(*ptep));
-               pfn = pte_pfn(*ptep);
-               pfn_valid = true;
-               /* call kvm_set_pfn_accessed() after unlock */
-       }
+
        if (write_fault && !pte_dirty(*ptep)) {
                if (!pte_write(*ptep)) {
                        ret = -EFAULT;
@@ -512,7 +507,6 @@ static int _kvm_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
 
                /* Track dirtying of writeable pages */
                set_pte(ptep, pte_mkdirty(*ptep));
-               pfn = pte_pfn(*ptep);
                mark_page_dirty(kvm, gfn);
        }
 
@@ -523,8 +517,6 @@ static int _kvm_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
 
 out:
        spin_unlock(&kvm->mmu_lock);
-       if (pfn_valid)
-               kvm_set_pfn_accessed(pfn);
        return ret;
 }