linux-kernel - [PATCH v12 68/84] KVM: MIPS: Mark "struct page" pfns dirty only in "slow" page fault path

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Message-ID: <20240726235234.228822-69-seanjc@google.com>
Date: Fri, 26 Jul 2024 16:52:17 -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 68/84] KVM: MIPS: Mark "struct page" pfns dirty only in
 "slow" page fault path

Mark pages/folios dirty only the slow page fault path, i.e. only when
mmu_lock is held and the operation is mmu_notifier-protected, as marking a
page/folio dirty after it has been written back can make some filesystems
unhappy (backing KVM guests will such filesystem files is uncommon, and
the race is minuscule, hence the lack of complaints).

See the link below for details.

Link: https://lore.kernel.org/all/cover.1683044162.git.lstoakes@gmail.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/mips/kvm/mmu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c
index c17157e700c0..4da9ce4eb54d 100644
--- a/arch/mips/kvm/mmu.c
+++ b/arch/mips/kvm/mmu.c
@@ -514,7 +514,6 @@ static int _kvm_mips_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa,
 		set_pte(ptep, pte_mkdirty(*ptep));
 		pfn = pte_pfn(*ptep);
 		mark_page_dirty(kvm, gfn);
-		kvm_set_pfn_dirty(pfn);
 	}
 
 	if (out_entry)
@@ -628,7 +627,6 @@ static int kvm_mips_map_page(struct kvm_vcpu *vcpu, unsigned long gpa,
 		if (write_fault) {
 			prot_bits |= __WRITEABLE;
 			mark_page_dirty(kvm, gfn);
-			kvm_set_pfn_dirty(pfn);
 		}
 	}
 	entry = pfn_pte(pfn, __pgprot(prot_bits));
@@ -642,6 +640,9 @@ static int kvm_mips_map_page(struct kvm_vcpu *vcpu, unsigned long gpa,
 	if (out_buddy)
 		*out_buddy = *ptep_buddy(ptep);
 
+	if (writeable)
+		kvm_set_pfn_dirty(pfn);
+
 	spin_unlock(&kvm->mmu_lock);
 	kvm_release_pfn_clean(pfn);
 	kvm_set_pfn_accessed(pfn);
-- 
2.46.0.rc1.232.g9752f9e123-goog