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

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Message-ID: <20240726235234.228822-70-seanjc@google.com>
Date: Fri, 26 Jul 2024 16:52:18 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>, 
	Michael Ellerman <mpe@...erman.id.au>, Anup Patel <anup@...infault.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, 
	Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, David Stevens <stevensd@...omium.org>
Subject: [PATCH v12 69/84] 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@...gle.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;
 }
 
-- 
2.46.0.rc1.232.g9752f9e123-goog