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(unknown [202.120.40.80]) by proxy188.sjtu.edu.cn (Postfix) with ESMTPSA id 5931837C955; Mon, 20 Jan 2025 20:05:29 +0800 (CST) From: Zheyun Shen To: thomas.lendacky@amd.com, seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de, kevinloughlin@google.com, mingo@redhat.com, bp@alien8.de Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Zheyun Shen Subject: [PATCH v5 3/3] KVM: SVM: Flush cache only on CPUs running SEV guest Date: Mon, 20 Jan 2025 20:05:03 +0800 Message-Id: <20250120120503.470533-4-szy0127@sjtu.edu.cn> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250120120503.470533-1-szy0127@sjtu.edu.cn> References: <20250120120503.470533-1-szy0127@sjtu.edu.cn> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On AMD CPUs without ensuring cache consistency, each memory page reclamation in an SEV guest triggers a call to wbinvd_on_all_cpus(), thereby affecting the performance of other programs on the host. Typically, an AMD server may have 128 cores or more, while the SEV guest might only utilize 8 of these cores. Meanwhile, host can use qemu-affinity to bind these 8 vCPUs to specific physical CPUs. Therefore, keeping a record of the physical core numbers each time a vCPU runs can help avoid flushing the cache for all CPUs every time. Suggested-by: Sean Christopherson Signed-off-by: Zheyun Shen --- arch/x86/kvm/svm/sev.c | 39 ++++++++++++++++++++++++++++++++++++--- arch/x86/kvm/svm/svm.c | 2 ++ arch/x86/kvm/svm/svm.h | 5 ++++- 3 files changed, 42 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 1ce67de9d..91469edd1 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -252,6 +252,36 @@ static void sev_asid_free(struct kvm_sev_info *sev) sev->misc_cg = NULL; } +static struct cpumask *sev_get_wbinvd_dirty_mask(struct kvm *kvm) +{ + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; + + return sev->wbinvd_dirty_mask; +} + +void sev_vcpu_load(struct kvm_vcpu *vcpu, int cpu) +{ + /* + * To optimize cache flushes when memory is reclaimed from an SEV VM, + * track physical CPUs that enter the guest for SEV VMs and thus can + * have encrypted, dirty data in the cache, and flush caches only for + * CPUs that have entered the guest. + */ + cpumask_set_cpu(cpu, sev_get_wbinvd_dirty_mask(vcpu->kvm)); +} + +static void sev_do_wbinvd(struct kvm *kvm) +{ + struct cpumask *dirty_mask = sev_get_wbinvd_dirty_mask(kvm); + + /* + * TODO: Clear CPUs from the bitmap prior to flushing. Doing so + * requires serializing multiple calls and having CPUs mark themselves + * "dirty" if they are currently running a vCPU for the VM. + */ + wbinvd_on_many_cpus(dirty_mask); +} + static void sev_decommission(unsigned int handle) { struct sev_data_decommission decommission; @@ -448,6 +478,8 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp, ret = sev_platform_init(&init_args); if (ret) goto e_free; + if (!zalloc_cpumask_var(&sev->wbinvd_dirty_mask, GFP_KERNEL_ACCOUNT)) + goto e_free; /* This needs to happen after SEV/SNP firmware initialization. */ if (vm_type == KVM_X86_SNP_VM) { @@ -2778,7 +2810,7 @@ int sev_mem_enc_unregister_region(struct kvm *kvm, * releasing the pages back to the system for use. CLFLUSH will * not do this, so issue a WBINVD. */ - wbinvd_on_all_cpus(); + sev_do_wbinvd(kvm); __unregister_enc_region_locked(kvm, region); @@ -2926,6 +2958,7 @@ void sev_vm_destroy(struct kvm *kvm) } sev_asid_free(sev); + free_cpumask_var(sev->wbinvd_dirty_mask); } void __init sev_set_cpu_caps(void) @@ -3129,7 +3162,7 @@ static void sev_flush_encrypted_page(struct kvm_vcpu *vcpu, void *va) return; do_wbinvd: - wbinvd_on_all_cpus(); + sev_do_wbinvd(vcpu->kvm); } void sev_guest_memory_reclaimed(struct kvm *kvm) @@ -3143,7 +3176,7 @@ void sev_guest_memory_reclaimed(struct kvm *kvm) if (!sev_guest(kvm) || sev_snp_guest(kvm)) return; - wbinvd_on_all_cpus(); + sev_do_wbinvd(kvm); } void sev_free_vcpu(struct kvm_vcpu *vcpu) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 21dacd312..d2a423c0e 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1565,6 +1565,8 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu) } if (kvm_vcpu_apicv_active(vcpu)) avic_vcpu_load(vcpu, cpu); + if (sev_guest(vcpu->kvm)) + sev_vcpu_load(vcpu, cpu); } static void svm_vcpu_put(struct kvm_vcpu *vcpu) diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 43fa6a16e..c8f42cb61 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -112,6 +112,8 @@ struct kvm_sev_info { void *guest_req_buf; /* Bounce buffer for SNP Guest Request input */ void *guest_resp_buf; /* Bounce buffer for SNP Guest Request output */ struct mutex guest_req_mutex; /* Must acquire before using bounce buffers */ + /* CPUs invoked VMRUN call wbinvd after guest memory is reclaimed */ + struct cpumask *wbinvd_dirty_mask; }; struct kvm_svm { @@ -763,6 +765,7 @@ void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu); int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order); void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end); int sev_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn); +void sev_vcpu_load(struct kvm_vcpu *vcpu, int cpu); #else static inline struct page *snp_safe_alloc_page_node(int node, gfp_t gfp) { @@ -793,7 +796,7 @@ static inline int sev_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn) { return 0; } - +static inline void sev_vcpu_load(struct kvm_vcpu *vcpu, int cpu) {} #endif /* vmenter.S */