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Thu, 10 Oct 2024 11:27:46 -0700 (PDT) Date: Thu, 10 Oct 2024 11:24:24 -0700 In-Reply-To: <20241010182427.1434605-1-seanjc@google.com> 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_Benn=C3=A9e?= " , Yan Zhao , David Matlack , David Stevens , Andrew Jones X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241010_112748_866197_677D122F X-CRM114-Status: GOOD ( 13.34 ) X-Spam-Score: -9.5 (---------) X-Spam-Report: Spam detection software, running on the system "bombadil.infradead.org", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: 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 p [...] Content analysis details: (-9.5 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:114a listed in] [list.dnswl.org] 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.0 SPF_PASS SPF: sender matches SPF record -7.5 USER_IN_DEF_DKIM_WL From: address is in the default DKIM welcome-list -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] -0.0 DKIMWL_WL_MED DKIMwl.org - Medium trust sender X-BeenThere: kvm-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Sender: "kvm-riscv" Errors-To: kvm-riscv-bounces+incoming=patchwork.ozlabs.org@lists.infradead.org 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 Bennée 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 = *sptep; int level = sptep_to_sp(sptep)->role.level; - struct page *page; 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; kvm_update_page_stats(kvm, level, -1); - - pfn = 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 = 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; } 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 kvm_mmu_page *root, tdp_mmu_iter_set_spte(kvm, &iter, SHADOW_NONPRESENT_VALUE); - 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.