From da3db168fb671f15e393b227f5c312c698ecb6ea Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 21 Mar 2023 18:14:39 -0700 Subject: [PATCH] KVM: x86: Virtualize FLUSH_L1D and passthrough MSR_IA32_FLUSH_CMD Virtualize FLUSH_L1D so that the guest can use the performant L1D flush if one of the many mitigations might require a flush in the guest, e.g. Linux provides an option to flush the L1D when switching mms. Passthrough MSR_IA32_FLUSH_CMD for write when it's supported in hardware and exposed to the guest, i.e. always let the guest write it directly if FLUSH_L1D is fully supported. Forward writes to hardware in host context on the off chance that KVM ends up emulating a WRMSR, or in the really unlikely scenario where userspace wants to force a flush. Restrict these forwarded WRMSRs to the known command out of an abundance of caution. Passing through the MSR means the guest can throw any and all values at hardware, but doing so in host context is arguably a bit more dangerous. Link: https://lkml.kernel.org/r/CALMp9eTt3xzAEoQ038bJQ9LN0ZOXrSWsN7xnNUD%2B0SS%3DWwF7Pg%40mail.gmail.com Link: https://lore.kernel.org/all/20230201132905.549148-2-eesposit@redhat.com Signed-off-by: Sean Christopherson Message-Id: <20230322011440.2195485-6-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/cpuid.c | 2 +- arch/x86/kvm/svm/svm.c | 5 +++++ arch/x86/kvm/vmx/nested.c | 3 +++ arch/x86/kvm/vmx/vmx.c | 5 +++++ arch/x86/kvm/vmx/vmx.h | 2 +- arch/x86/kvm/x86.c | 12 ++++++++++++ 6 files changed, 27 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 599aebec2d52c..9583a110cf5f2 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -653,7 +653,7 @@ void kvm_set_cpu_caps(void) F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) | F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM) | F(SERIALIZE) | F(TSXLDTRK) | F(AVX512_FP16) | - F(AMX_TILE) | F(AMX_INT8) | F(AMX_BF16) + F(AMX_TILE) | F(AMX_INT8) | F(AMX_BF16) | F(FLUSH_L1D) ); /* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software. */ diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 85bb535fc3213..b32edaf5a74b7 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -95,6 +95,7 @@ static const struct svm_direct_access_msrs { #endif { .index = MSR_IA32_SPEC_CTRL, .always = false }, { .index = MSR_IA32_PRED_CMD, .always = false }, + { .index = MSR_IA32_FLUSH_CMD, .always = false }, { .index = MSR_IA32_LASTBRANCHFROMIP, .always = false }, { .index = MSR_IA32_LASTBRANCHTOIP, .always = false }, { .index = MSR_IA32_LASTINTFROMIP, .always = false }, @@ -4140,6 +4141,10 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PRED_CMD, 0, !!guest_has_pred_cmd_msr(vcpu)); + if (boot_cpu_has(X86_FEATURE_FLUSH_L1D)) + set_msr_interception(vcpu, svm->msrpm, MSR_IA32_FLUSH_CMD, 0, + !!guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D)); + /* For sev guests, the memory encryption bit is not reserved in CR3. */ if (sev_guest(vcpu->kvm)) { best = kvm_find_cpuid_entry(vcpu, 0x8000001F); diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 1bc2b80273c97..f63b28f46a713 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -654,6 +654,9 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu, nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0, MSR_IA32_PRED_CMD, MSR_TYPE_W); + nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0, + MSR_IA32_FLUSH_CMD, MSR_TYPE_W); + kvm_vcpu_unmap(vcpu, &vmx->nested.msr_bitmap_map, false); vmx->nested.force_msr_bitmap_recalc = false; diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 29807be219b97..56e0c7ae961d3 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -164,6 +164,7 @@ module_param(allow_smaller_maxphyaddr, bool, S_IRUGO); static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = { MSR_IA32_SPEC_CTRL, MSR_IA32_PRED_CMD, + MSR_IA32_FLUSH_CMD, MSR_IA32_TSC, #ifdef CONFIG_X86_64 MSR_FS_BASE, @@ -7720,6 +7721,10 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) vmx_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W, !guest_has_pred_cmd_msr(vcpu)); + if (boot_cpu_has(X86_FEATURE_FLUSH_L1D)) + vmx_set_intercept_for_msr(vcpu, MSR_IA32_FLUSH_CMD, MSR_TYPE_W, + !guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D)); + set_cr4_guest_host_mask(vmx); vmx_write_encls_bitmap(vcpu, NULL); diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 2acdc54bc34b1..cb766f65a3ebc 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -369,7 +369,7 @@ struct vcpu_vmx { struct lbr_desc lbr_desc; /* Save desired MSR intercept (read: pass-through) state */ -#define MAX_POSSIBLE_PASSTHROUGH_MSRS 15 +#define MAX_POSSIBLE_PASSTHROUGH_MSRS 16 struct { DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS); DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c83ec88da0434..3c58dbae7b4c7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3628,6 +3628,18 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB); break; + case MSR_IA32_FLUSH_CMD: + if (!msr_info->host_initiated && + !guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D)) + return 1; + + if (!boot_cpu_has(X86_FEATURE_FLUSH_L1D) || (data & ~L1D_FLUSH)) + return 1; + if (!data) + break; + + wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH); + break; case MSR_EFER: return set_efer(vcpu, msr_info); case MSR_K7_HWCR: -- 2.30.2