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Thu, 10 Oct 2024 11:27:46 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 10 Oct 2024 11:24:24 -0700 In-Reply-To: <20241010182427.1434605-1-seanjc@google.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: Mime-Version: 1.0 References: <20241010182427.1434605-1-seanjc@google.com> X-Mailer: git-send-email 2.47.0.rc1.288.g06298d1525-goog Message-ID: <20241010182427.1434605-83-seanjc@google.com> Subject: [PATCH v13 82/85] KVM: x86/mmu: Don't mark "struct page" accessed when zapping SPTEs From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Sean Christopherson Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, "=?UTF-8?q?Alex=20Benn=C3=A9e?=" , Yan Zhao , David Matlack , David Stevens , Andrew Jones Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Don't mark pages/folios as accessed in the primary MMU when zapping SPTEs, as doing so relies on kvm_pfn_to_refcounted_page(), and generally speaking is unnecessary and wasteful. KVM participates in page aging via mmu_notifiers, so there's no need to push "accessed" updates to the primary MMU. And if KVM zaps a SPTe in response to an mmu_notifier, marking it accessed _after_ the primary MMU has decided to zap the page is likely to go unnoticed, i.e. odds are good that, if the page is being zapped for reclaim, the page will be swapped out regardless of whether or not KVM marks the page accessed. Dropping x86's use of kvm_set_pfn_accessed() also paves the way for removing kvm_pfn_to_refcounted_page() and all its users. Tested-by: Alex Benn=C3=A9e Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 17 ----------------- arch/x86/kvm/mmu/tdp_mmu.c | 3 --- 2 files changed, 20 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 5acdaf3b1007..55eeca931e23 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -559,10 +559,8 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte) */ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep) { - kvm_pfn_t pfn; u64 old_spte =3D *sptep; int level =3D sptep_to_sp(sptep)->role.level; - struct page *page; =20 if (!is_shadow_present_pte(old_spte) || !spte_has_volatile_bits(old_spte)) @@ -574,21 +572,6 @@ static u64 mmu_spte_clear_track_bits(struct kvm *kvm, = u64 *sptep) return old_spte; =20 kvm_update_page_stats(kvm, level, -1); - - pfn =3D spte_to_pfn(old_spte); - - /* - * KVM doesn't hold a reference to any pages mapped into the guest, and - * instead uses the mmu_notifier to ensure that KVM unmaps any pages - * before they are reclaimed. Sanity check that, if the pfn is backed - * by a refcounted page, the refcount is elevated. - */ - page =3D kvm_pfn_to_refcounted_page(pfn); - WARN_ON_ONCE(page && !page_count(page)); - - if (is_accessed_spte(old_spte)) - kvm_set_pfn_accessed(pfn); - return old_spte; } =20 diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 8aa0d7a7602b..91caa73a905b 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -861,9 +861,6 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct k= vm_mmu_page *root, =20 tdp_mmu_iter_set_spte(kvm, &iter, SHADOW_NONPRESENT_VALUE); =20 - if (is_accessed_spte(iter.old_spte)) - kvm_set_pfn_accessed(spte_to_pfn(iter.old_spte)); - /* * Zappings SPTEs in invalid roots doesn't require a TLB flush, * see kvm_tdp_mmu_zap_invalidated_roots() for details. --=20 2.47.0.rc1.288.g06298d1525-goog