[PATCH v12 69/84] KVM: MIPS: Mark "struct page" pfns accessed only in "slow" page fault path

Sean Christopherson
2024-07-27T00:28:43Z

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>
---
arch/mips/kvm/mmu.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c
index 4da9ce4eb54d..f1e4b618ec6d 100644
--- 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;
}