Commit 0fe133a3 authored Oct 10, 2024 by Sean Christopherson Committed by Paolo Bonzini Oct 25, 2024

KVM: LoongArch: 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


Reviewed-by: Bibo Mao <maobibo@loongson.cn>
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: <20241010182427.1434605-66-seanjc@google.com>

parent 8b135c77

arch/loongarch/kvm/mmu.c

+9 −7

Original line number	Diff line number	Diff line
		@@ -608,13 +608,13 @@ static int kvm_map_page_fast(struct kvm_vcpu *vcpu, unsigned long gpa, bool writ
		if (kvm_pte_young(changed))
		kvm_set_pfn_accessed(pfn);

		if (kvm_pte_dirty(changed)) {
		mark_page_dirty(kvm, gfn);
		kvm_set_pfn_dirty(pfn);
		}
		if (page)
		put_page(page);
		}

		if (kvm_pte_dirty(changed))
		mark_page_dirty(kvm, gfn);

		return ret;
		out:
		spin_unlock(&kvm->mmu_lock);
		@@ -915,12 +915,14 @@ static int kvm_map_page(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
		else
		++kvm->stat.pages;
		kvm_set_pte(ptep, new_pte);

		if (writeable)
		kvm_set_pfn_dirty(pfn);

		spin_unlock(&kvm->mmu_lock);

		if (prot_bits & _PAGE_DIRTY) {
		if (prot_bits & _PAGE_DIRTY)
		mark_page_dirty_in_slot(kvm, memslot, gfn);
		kvm_set_pfn_dirty(pfn);
		}

		kvm_release_pfn_clean(pfn);
		out: