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AJvYcCWX90i3xDKlAyTiWoXIwk0afvAobw6H0W3KcTAMlXhKGn5MIe9l/geNqTTAleolMg/t2XGKbOMZb84XT7l/O9MfD5umUwMoUrI/ X-Gm-Message-State: AOJu0YydZ6UiY7zWlUd5H4HWpkL5RBXVBaaLJtoF6D5b93E/4wpOky7c 8sP7IqEPaUG53FBlCTNRcHhCD5IYneKVZ0+gCtbIvZxDI59NkTK+hpwVy4Znta1P6dsasdeNNf/ yWw== X-Google-Smtp-Source: AGHT+IGyG+mtcr/kVU3oAvt9em/qYRB1UDjtYQnTl1yJOreZRmpK01aFGB2+hznOEVLDsABe9yFV/Tj5WtE= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6902:100f:b0:df7:8c1b:430a with SMTP id 3f1490d57ef6-dfe65e7eb4dmr855641276.3.1718228489057; Wed, 12 Jun 2024 14:41:29 -0700 (PDT) Date: Wed, 12 Jun 2024 14:41:27 -0700 In-Reply-To: <20240207172646.3981-9-xin3.li@intel.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240207172646.3981-1-xin3.li@intel.com> <20240207172646.3981-9-xin3.li@intel.com> Message-ID: Subject: Re: [PATCH v2 08/25] KVM: VMX: Initialize VMCS FRED fields From: Sean Christopherson To: Xin Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, pbonzini@redhat.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, shuah@kernel.org, vkuznets@redhat.com, peterz@infradead.org, ravi.v.shankar@intel.com, xin@zytor.com Content-Type: text/plain; charset="us-ascii" On Wed, Feb 07, 2024, Xin Li wrote: > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index d58ed2d3d379..b7b772183ee4 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -1470,6 +1470,18 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, > (unsigned long)(cpu_entry_stack(cpu) + 1)); > } > > +#ifdef CONFIG_X86_64 Don't bother, practically no one cares about 32-bit KVM these days, and I highly don't anyone that runs 32-bit KVM cares about the code footprint to this degree. > + /* Per-CPU FRED MSRs */ > + if (kvm_cpu_cap_has(X86_FEATURE_FRED)) { > + vmcs_write64(HOST_IA32_FRED_RSP1, read_msr(MSR_IA32_FRED_RSP1)); > + vmcs_write64(HOST_IA32_FRED_RSP2, read_msr(MSR_IA32_FRED_RSP2)); > + vmcs_write64(HOST_IA32_FRED_RSP3, read_msr(MSR_IA32_FRED_RSP3)); > + vmcs_write64(HOST_IA32_FRED_SSP1, read_msr(MSR_IA32_FRED_SSP1)); > + vmcs_write64(HOST_IA32_FRED_SSP2, read_msr(MSR_IA32_FRED_SSP2)); > + vmcs_write64(HOST_IA32_FRED_SSP3, read_msr(MSR_IA32_FRED_SSP3)); That's a lot of RDMSRs to eat on every task migration. How hard would it be to add a per-CPU cache for each of these? Or is there a pre-existing way to get at the info that's faster than RDMSR? > + } > +#endif > + > vmx->loaded_vmcs->cpu = cpu; > } > } > @@ -4321,6 +4333,15 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx) > */ > vmcs_write16(HOST_DS_SELECTOR, 0); > vmcs_write16(HOST_ES_SELECTOR, 0); > + > + /* > + * FRED MSRs are per-cpu, however FRED CONFIG and STKLVLS MSRs > + * are the same on all CPUs, thus they are initialized here. Eh, just trim this to: /* FRED CONFIG and STKLVLS are the same on all CPUs. */ > + */ > + if (kvm_cpu_cap_has(X86_FEATURE_FRED)) { > + vmcs_write64(HOST_IA32_FRED_CONFIG, read_msr(MSR_IA32_FRED_CONFIG)); > + vmcs_write64(HOST_IA32_FRED_STKLVLS, read_msr(MSR_IA32_FRED_STKLVLS)); > + } > #else > vmcs_write16(HOST_DS_SELECTOR, __KERNEL_DS); /* 22.2.4 */ > vmcs_write16(HOST_ES_SELECTOR, __KERNEL_DS); /* 22.2.4 */ > @@ -4865,6 +4886,19 @@ static void __vmx_vcpu_reset(struct kvm_vcpu *vcpu) > */ > vmx->pi_desc.nv = POSTED_INTR_VECTOR; > vmx->pi_desc.sn = 1; > + > +#ifdef CONFIG_X86_64 > + if (kvm_cpu_cap_has(X86_FEATURE_FRED)) { > + vmcs_write64(GUEST_IA32_FRED_CONFIG, 0); > + vmcs_write64(GUEST_IA32_FRED_RSP1, 0); > + vmcs_write64(GUEST_IA32_FRED_RSP2, 0); > + vmcs_write64(GUEST_IA32_FRED_RSP3, 0); > + vmcs_write64(GUEST_IA32_FRED_STKLVLS, 0); > + vmcs_write64(GUEST_IA32_FRED_SSP1, 0); > + vmcs_write64(GUEST_IA32_FRED_SSP2, 0); > + vmcs_write64(GUEST_IA32_FRED_SSP3, 0); > + } Somewhat of a moot point, but this belongs in init_vmcs(), not __vmx_vcpu_reset().