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>

Author: sean-jc

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;
 }