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Peter Anvin" , kvm@vger.kernel.org Subject: [PATCH 1/2] kvm: x86/mmu: Reduce the update to the spte in FNAME(sync_page) Date: Mon, 12 Dec 2022 23:32:04 +0800 Message-Id: <20221212153205.3360-2-jiangshanlai@gmail.com> X-Mailer: git-send-email 2.19.1.6.gb485710b In-Reply-To: <20221212153205.3360-1-jiangshanlai@gmail.com> References: <20221212153205.3360-1-jiangshanlai@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1752023048276171446?= X-GMAIL-MSGID: =?utf-8?q?1752023048276171446?= From: Lai Jiangshan Sometimes when the guest updates its pagetable, it adds only new gptes to it without changing any existed one, so there is no point to update the sptes for these existed gptes. Also when the sptes for these unchanged gptes are updated, the AD bits are also removed since make_spte() is called with prefetch=true which might result unneeded TLB flushing. Do nothing if the permissions are unchanged or only write-access is being added. Only update the spte when write-access is being removed. Drop the SPTE otherwise. Signed-off-by: Lai Jiangshan --- arch/x86/kvm/mmu/paging_tmpl.h | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index e5662dbd519c..613f043a3e9e 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -1023,7 +1023,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) for (i = 0; i < SPTE_ENT_PER_PAGE; i++) { u64 *sptep, spte; struct kvm_memory_slot *slot; - unsigned pte_access; + unsigned old_pte_access, pte_access; pt_element_t gpte; gpa_t pte_gpa; gfn_t gfn; @@ -1064,6 +1064,23 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) continue; } + /* + * Drop the SPTE if the new protections would result in access + * permissions other than write-access is changing. Do nothing + * if the permissions are unchanged or only write-access is + * being added. Only update the spte when write-access is being + * removed. + */ + old_pte_access = kvm_mmu_page_get_access(sp, i); + if (old_pte_access == pte_access || + (old_pte_access | ACC_WRITE_MASK) == pte_access) + continue; + if (old_pte_access != (pte_access | ACC_WRITE_MASK)) { + drop_spte(vcpu->kvm, &sp->spt[i]); + flush = true; + continue; + } + /* Update the shadowed access bits in case they changed. */ kvm_mmu_page_set_access(sp, i, pte_access); From patchwork Mon Dec 12 15:32:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lai Jiangshan X-Patchwork-Id: 32422 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:f944:0:0:0:0:0 with SMTP id q4csp2309993wrr; Mon, 12 Dec 2022 07:36:03 -0800 (PST) X-Google-Smtp-Source: AA0mqf5TSwao8h9UFXxV/E3HIy1euyuf8asnJGY42oZaF8LMPkyOthrGlclK5X1GKrpRJk0OSDAk X-Received: by 2002:a17:906:e297:b0:7c0:af5d:c54c with SMTP id gg23-20020a170906e29700b007c0af5dc54cmr14656833ejb.77.1670859363458; Mon, 12 Dec 2022 07:36:03 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1670859363; cv=none; d=google.com; s=arc-20160816; b=gw6/7gmuVnQzG1N5RIqK2iKLiM2fg0YQjN6qamvI0oPQU6Um+WnI8mFbpucc7R9i10 sqR21mspC8BQXW6GrFuIYrxm19DqA4B+fxPwq7hE+uAv7BKxe8jYKREmLN6oDBh3jIhX 9WtAPuVHeaTtE/jaU9goBBzH0LefNC4yAwDWGHX/e0mVKvWaWUWM7aiENsgKd6FNyHH3 kdWzivPvCVaKedgWnzWrpMu94X7xUfcKghH61Cmd7BfLaxvRPy0+KV7hONQlsBAlW845 wmgBNQ3vkAPNpz7UGLWCC9I+8zUHuHRyyRtzYqJG3nfq+3TLSrXZJi2fKcEw26GXv5m4 t0RA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=+/jm7VnVwXNJnon7L3mSgLc+ja6eHEtRF1Bkw57lTnY=; b=TkjNthL5PkJG4uidXw8fwNnKpMlgzaztVu+kYTwP0b2En2LWG/mqy7IT6HrXAMX+7V VxoPii5rIgT7l2lNU7S1DCZnV4etygDM8dVKgrvED7XevmZt7BY1YGRDdVX8QVeUh4uG j/WSCHphppfmLGkArSUiL8xbtjBBt0n8V5NWrXnbELfBQAvYo5+zWwkNlTWkcTqZynJm MugqSef08WUf85IRsZG000LHKzyHCK++FG2OrfRzPrU1551m+egGEtKMj6geu6fFs1bo JRqQ+ClY0RL4xJf/vggRJ5EKaswbYEWHVF1G4aAgLtCn7zTG19JUvaSPN8YP3o2i0Xx3 3EAw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=Bfu11zCO; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: from out1.vger.email (out1.vger.email. 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Peter Anvin" , kvm@vger.kernel.org Subject: [PATCH 2/2] kvm: x86/mmu: Remove useless shadow_host_writable_mask Date: Mon, 12 Dec 2022 23:32:05 +0800 Message-Id: <20221212153205.3360-3-jiangshanlai@gmail.com> X-Mailer: git-send-email 2.19.1.6.gb485710b In-Reply-To: <20221212153205.3360-1-jiangshanlai@gmail.com> References: <20221212153205.3360-1-jiangshanlai@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1752023027936945842?= X-GMAIL-MSGID: =?utf-8?q?1752023027936945842?= From: Lai Jiangshan shadow_host_writable_mask is only used in FNAME(sync_page) which doesn't actually need it. Remove it and release a bit from spte. Signed-off-by: Lai Jiangshan --- arch/x86/kvm/mmu/paging_tmpl.h | 7 ++++++- arch/x86/kvm/mmu/spte.c | 8 +------ arch/x86/kvm/mmu/spte.h | 38 +++++++++++----------------------- 3 files changed, 19 insertions(+), 34 deletions(-) diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 613f043a3e9e..8b83abf1d8bc 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -1084,9 +1084,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp) /* Update the shadowed access bits in case they changed. */ kvm_mmu_page_set_access(sp, i, pte_access); + /* + * It doesn't matter whether it is host_writable or not since + * write-access is being removed. + */ + host_writable = false; + sptep = &sp->spt[i]; spte = *sptep; - host_writable = spte & shadow_host_writable_mask; slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn); make_spte(vcpu, sp, slot, pte_access, gfn, spte_to_pfn(spte), spte, true, false, diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c index c0fd7e049b4e..00c88b1dca0a 100644 --- a/arch/x86/kvm/mmu/spte.c +++ b/arch/x86/kvm/mmu/spte.c @@ -24,7 +24,6 @@ static bool __ro_after_init allow_mmio_caching; module_param_named(mmio_caching, enable_mmio_caching, bool, 0444); EXPORT_SYMBOL_GPL(enable_mmio_caching); -u64 __read_mostly shadow_host_writable_mask; u64 __read_mostly shadow_mmu_writable_mask; u64 __read_mostly shadow_nx_mask; u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */ @@ -192,9 +191,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, if (shadow_memtype_mask) spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn, kvm_is_mmio_pfn(pfn)); - if (host_writable) - spte |= shadow_host_writable_mask; - else + if (!host_writable) pte_access &= ~ACC_WRITE_MASK; if (shadow_me_value && !kvm_is_mmio_pfn(pfn)) @@ -332,7 +329,6 @@ u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn) new_spte |= (u64)new_pfn << PAGE_SHIFT; new_spte &= ~PT_WRITABLE_MASK; - new_spte &= ~shadow_host_writable_mask; new_spte &= ~shadow_mmu_writable_mask; new_spte = mark_spte_for_access_track(new_spte); @@ -440,7 +436,6 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only) */ shadow_memtype_mask = VMX_EPT_MT_MASK | VMX_EPT_IPAT_BIT; shadow_acc_track_mask = VMX_EPT_RWX_MASK; - shadow_host_writable_mask = EPT_SPTE_HOST_WRITABLE; shadow_mmu_writable_mask = EPT_SPTE_MMU_WRITABLE; /* @@ -500,7 +495,6 @@ void kvm_mmu_reset_all_pte_masks(void) shadow_me_mask = 0; shadow_me_value = 0; - shadow_host_writable_mask = DEFAULT_SPTE_HOST_WRITABLE; shadow_mmu_writable_mask = DEFAULT_SPTE_MMU_WRITABLE; /* diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h index 1f03701b943a..9824b33539c9 100644 --- a/arch/x86/kvm/mmu/spte.h +++ b/arch/x86/kvm/mmu/spte.h @@ -75,8 +75,7 @@ static_assert(!(SPTE_TDP_AD_MASK & SHADOW_ACC_TRACK_SAVED_MASK)); * SPTE is write-protected. See is_writable_pte() for details. */ -/* Bits 9 and 10 are ignored by all non-EPT PTEs. */ -#define DEFAULT_SPTE_HOST_WRITABLE BIT_ULL(9) +/* Bit 10 are ignored by all non-EPT PTEs. */ #define DEFAULT_SPTE_MMU_WRITABLE BIT_ULL(10) /* @@ -84,12 +83,9 @@ static_assert(!(SPTE_TDP_AD_MASK & SHADOW_ACC_TRACK_SAVED_MASK)); * to not overlap the A/D type mask or the saved access bits of access-tracked * SPTEs when A/D bits are disabled. */ -#define EPT_SPTE_HOST_WRITABLE BIT_ULL(57) #define EPT_SPTE_MMU_WRITABLE BIT_ULL(58) -static_assert(!(EPT_SPTE_HOST_WRITABLE & SPTE_TDP_AD_MASK)); static_assert(!(EPT_SPTE_MMU_WRITABLE & SPTE_TDP_AD_MASK)); -static_assert(!(EPT_SPTE_HOST_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK)); static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK)); /* Defined only to keep the above static asserts readable. */ @@ -148,7 +144,6 @@ static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 11); #define MMIO_SPTE_GEN_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0) -extern u64 __read_mostly shadow_host_writable_mask; extern u64 __read_mostly shadow_mmu_writable_mask; extern u64 __read_mostly shadow_nx_mask; extern u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */ @@ -383,27 +378,23 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check, * * For cases #1 and #4, KVM can safely make such SPTEs writable without taking * mmu_lock as capturing the Accessed/Dirty state doesn't require taking it. - * To differentiate #1 and #4 from #2 and #3, KVM uses two software-only bits + * To differentiate #1 and #4 from #2 and #3, KVM uses a software-only bit * in the SPTE: * * shadow_mmu_writable_mask, aka MMU-writable - * Cleared on SPTEs that KVM is currently write-protecting for shadow paging * purposes (case 2 above). - * - * shadow_host_writable_mask, aka Host-writable - * Cleared on SPTEs that are not host-writable (case 3 above) * - * Note, not all possible combinations of PT_WRITABLE_MASK, - * shadow_mmu_writable_mask, and shadow_host_writable_mask are valid. A given - * SPTE can be in only one of the following states, which map to the - * aforementioned 3 cases: + * Note, not all possible combinations of PT_WRITABLE_MASK and + * shadow_mmu_writable_mask are valid. A given SPTE can be in only one of the + * following states, which map to the aforementioned 3 cases: * - * shadow_host_writable_mask | shadow_mmu_writable_mask | PT_WRITABLE_MASK - * ------------------------- | ------------------------ | ---------------- - * 1 | 1 | 1 (writable) - * 1 | 1 | 0 (case 1) - * 1 | 0 | 0 (case 2) - * 0 | 0 | 0 (case 3) + * shadow_mmu_writable_mask | PT_WRITABLE_MASK + * ------------------------ | ---------------- + * 1 | 1 (writable) + * 1 | 0 (case 1) + * 0 | 0 (case 2,3) * * The valid combinations of these bits are checked by * check_spte_writable_invariants() whenever an SPTE is modified. @@ -433,13 +424,8 @@ static inline bool is_writable_pte(unsigned long pte) /* Note: spte must be a shadow-present leaf SPTE. */ static inline void check_spte_writable_invariants(u64 spte) { - if (spte & shadow_mmu_writable_mask) - WARN_ONCE(!(spte & shadow_host_writable_mask), - "kvm: MMU-writable SPTE is not Host-writable: %llx", - spte); - else - WARN_ONCE(is_writable_pte(spte), - "kvm: Writable SPTE is not MMU-writable: %llx", spte); + WARN_ONCE(!(spte & shadow_mmu_writable_mask) && is_writable_pte(spte), + "kvm: Writable SPTE is not MMU-writable: %llx", spte); } static inline bool is_mmu_writable_spte(u64 spte)