3.16.57-rc1 review patch. If anyone has any objections, please let me know.
------------------ From: KarimAllah Ahmed <[email protected]> commit d28b387fb74da95d69d2615732f50cceb38e9a4d upstream. [ Based on a patch from Ashok Raj <[email protected]> ] Add direct access to MSR_IA32_SPEC_CTRL for guests. This is needed for guests that will only mitigate Spectre V2 through IBRS+IBPB and will not be using a retpoline+IBPB based approach. To avoid the overhead of saving and restoring the MSR_IA32_SPEC_CTRL for guests that do not actually use the MSR, only start saving and restoring when a non-zero is written to it. No attempt is made to handle STIBP here, intentionally. Filtering STIBP may be added in a future patch, which may require trapping all writes if we don't want to pass it through directly to the guest. [dwmw2: Clean up CPUID bits, save/restore manually, handle reset] Signed-off-by: KarimAllah Ahmed <[email protected]> Signed-off-by: David Woodhouse <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Reviewed-by: Darren Kenny <[email protected]> Reviewed-by: Konrad Rzeszutek Wilk <[email protected]> Reviewed-by: Jim Mattson <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Jun Nakajima <[email protected]> Cc: [email protected] Cc: Dave Hansen <[email protected]> Cc: Tim Chen <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Asit Mallick <[email protected]> Cc: Arjan Van De Ven <[email protected]> Cc: Greg KH <[email protected]> Cc: Paolo Bonzini <[email protected]> Cc: Dan Williams <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Ashok Raj <[email protected]> Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: David Woodhouse <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> [bwh: Backported to 3.16: - No support for nested MSR bitmaps - Adjust context] Signed-off-by: Ben Hutchings <[email protected]> --- arch/x86/kvm/cpuid.c | 8 +++--- arch/x86/kvm/cpuid.h | 11 ++++++++ arch/x86/kvm/vmx.c | 64 ++++++++++++++++++++++++++++++++++++++++++++ arch/x86/kvm/x86.c | 2 +- 4 files changed, 81 insertions(+), 4 deletions(-) --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -302,7 +302,7 @@ static inline int __do_cpuid_ent(struct /* cpuid 0x80000008.ebx */ const u32 kvm_cpuid_8000_0008_ebx_x86_features = - F(IBPB); + F(IBPB) | F(IBRS); /* cpuid 0xC0000001.edx */ const u32 kvm_supported_word5_x86_features = @@ -318,7 +318,7 @@ static inline int __do_cpuid_ent(struct /* cpuid 7.0.edx*/ const u32 kvm_cpuid_7_0_edx_x86_features = - F(ARCH_CAPABILITIES); + F(SPEC_CTRL) | F(ARCH_CAPABILITIES); /* all calls to cpuid_count() should be made on the same cpu */ get_cpu(); @@ -524,9 +524,11 @@ static inline int __do_cpuid_ent(struct g_phys_as = phys_as; entry->eax = g_phys_as | (virt_as << 8); entry->edx = 0; - /* IBPB isn't necessarily present in hardware cpuid */ + /* IBRS and IBPB aren't necessarily present in hardware cpuid */ if (boot_cpu_has(X86_FEATURE_IBPB)) entry->ebx |= F(IBPB); + if (boot_cpu_has(X86_FEATURE_IBRS)) + entry->ebx |= F(IBRS); entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features; cpuid_mask(&entry->ebx, 11); break; --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -115,6 +115,17 @@ static inline bool guest_cpuid_has_ibpb( return best && (best->edx & bit(X86_FEATURE_SPEC_CTRL)); } +static inline bool guest_cpuid_has_ibrs(struct kvm_vcpu *vcpu) +{ + struct kvm_cpuid_entry2 *best; + + best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0); + if (best && (best->ebx & bit(X86_FEATURE_IBRS))) + return true; + best = kvm_find_cpuid_entry(vcpu, 7, 0); + return best && (best->edx & bit(X86_FEATURE_SPEC_CTRL)); +} + static inline bool guest_cpuid_has_arch_capabilities(struct kvm_vcpu *vcpu) { struct kvm_cpuid_entry2 *best; --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -433,6 +433,7 @@ struct vcpu_vmx { #endif u64 arch_capabilities; + u64 spec_ctrl; u32 vm_entry_controls_shadow; u32 vm_exit_controls_shadow; @@ -2524,6 +2525,13 @@ static int vmx_get_msr(struct kvm_vcpu * case MSR_IA32_TSC: msr_info->data = guest_read_tsc(); break; + case MSR_IA32_SPEC_CTRL: + if (!msr_info->host_initiated && + !guest_cpuid_has_ibrs(vcpu)) + return 1; + + msr_info->data = to_vmx(vcpu)->spec_ctrl; + break; case MSR_IA32_ARCH_CAPABILITIES: if (!msr_info->host_initiated && !guest_cpuid_has_arch_capabilities(vcpu)) @@ -2622,6 +2630,36 @@ static int vmx_set_msr(struct kvm_vcpu * case MSR_IA32_TSC: kvm_write_tsc(vcpu, msr_info); break; + case MSR_IA32_SPEC_CTRL: + if (!msr_info->host_initiated && + !guest_cpuid_has_ibrs(vcpu)) + return 1; + + /* The STIBP bit doesn't fault even if it's not advertised */ + if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP)) + return 1; + + vmx->spec_ctrl = data; + + if (!data) + break; + + /* + * For non-nested: + * When it's written (to non-zero) for the first time, pass + * it through. + * + * For nested: + * The handling of the MSR bitmap for L2 guests is done in + * nested_vmx_merge_msr_bitmap. We should not touch the + * vmcs02.msr_bitmap here since it gets completely overwritten + * in the merging. We update the vmcs01 here for L1 as well + * since it will end up touching the MSR anyway now. + */ + vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap, + MSR_IA32_SPEC_CTRL, + MSR_TYPE_RW); + break; case MSR_IA32_PRED_CMD: if (!msr_info->host_initiated && !guest_cpuid_has_ibpb(vcpu)) @@ -4617,6 +4655,7 @@ static void vmx_vcpu_reset(struct kvm_vc struct msr_data apic_base_msr; vmx->rmode.vm86_active = 0; + vmx->spec_ctrl = 0; vmx->soft_vnmi_blocked = 0; @@ -7496,6 +7535,15 @@ static void __noclone vmx_vcpu_run(struc atomic_switch_perf_msrs(vmx); debugctlmsr = get_debugctlmsr(); + /* + * If this vCPU has touched SPEC_CTRL, restore the guest's value if + * it's non-zero. Since vmentry is serialising on affected CPUs, there + * is no need to worry about the conditional branch over the wrmsr + * being speculatively taken. + */ + if (vmx->spec_ctrl) + wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); + vmx->__launched = vmx->loaded_vmcs->launched; asm( /* Store host registers */ @@ -7614,6 +7662,22 @@ static void __noclone vmx_vcpu_run(struc #endif ); + /* + * We do not use IBRS in the kernel. If this vCPU has used the + * SPEC_CTRL MSR it may have left it on; save the value and + * turn it off. This is much more efficient than blindly adding + * it to the atomic save/restore list. Especially as the former + * (Saving guest MSRs on vmexit) doesn't even exist in KVM. + * + * If the L01 MSR bitmap does not intercept the MSR, then we need to + * save it. + */ + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_SPEC_CTRL)) + rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); + + if (vmx->spec_ctrl) + wrmsrl(MSR_IA32_SPEC_CTRL, 0); + /* Eliminate branch target predictions from guest mode */ vmexit_fill_RSB(); --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -894,7 +894,7 @@ static u32 msrs_to_save[] = { #endif MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA, MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS, - MSR_IA32_ARCH_CAPABILITIES + MSR_IA32_SPEC_CTRL, MSR_IA32_ARCH_CAPABILITIES }; static unsigned num_msrs_to_save;
