From: KarimAllah Ahmed karahmed@amazon.de
[ Based on a patch from Ashok Raj ashok.raj@intel.com ]
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 karahmed@amazon.de Signed-off-by: David Woodhouse dwmw@amazon.co.uk Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Darren Kenny darren.kenny@oracle.com Reviewed-by: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Reviewed-by: Jim Mattson jmattson@google.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Andi Kleen ak@linux.intel.com Cc: Jun Nakajima jun.nakajima@intel.com Cc: kvm@vger.kernel.org Cc: Dave Hansen dave.hansen@intel.com Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Andy Lutomirski luto@kernel.org Cc: Asit Mallick asit.k.mallick@intel.com Cc: Arjan Van De Ven arjan.van.de.ven@intel.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Paolo Bonzini pbonzini@redhat.com Cc: Dan Williams dan.j.williams@intel.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Ashok Raj ashok.raj@intel.com Link: https://lkml.kernel.org/r/1517522386-18410-5-git-send-email-karahmed@amazon....
(cherry picked from commit d28b387fb74da95d69d2615732f50cceb38e9a4d) Signed-off-by: David Woodhouse dwmw@amazon.co.uk --- arch/x86/kvm/cpuid.c | 8 ++-- arch/x86/kvm/cpuid.h | 11 ++++++ arch/x86/kvm/vmx.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++- arch/x86/kvm/x86.c | 2 +- 4 files changed, 118 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 9c6493f..93f924d 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -357,7 +357,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
/* cpuid 0x80000008.ebx */ const u32 kvm_cpuid_8000_0008_ebx_x86_features = - F(IBPB); + F(IBPB) | F(IBRS);
/* cpuid 0xC0000001.edx */ const u32 kvm_cpuid_C000_0001_edx_x86_features = @@ -382,7 +382,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
/* 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(); @@ -618,9 +618,11 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, 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, CPUID_8000_0008_EBX); break; diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h index 8719997..d1beb71 100644 --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -171,6 +171,17 @@ static inline bool guest_cpuid_has_ibpb(struct kvm_vcpu *vcpu) 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; diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 92bf61f..764cb7c 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -552,6 +552,7 @@ struct vcpu_vmx { #endif
u64 arch_capabilities; + u64 spec_ctrl;
u32 vm_entry_controls_shadow; u32 vm_exit_controls_shadow; @@ -1852,6 +1853,29 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) }
/* + * Check if MSR is intercepted for currently loaded MSR bitmap. + */ +static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr) +{ + unsigned long *msr_bitmap; + int f = sizeof(unsigned long); + + if (!cpu_has_vmx_msr_bitmap()) + return true; + + msr_bitmap = to_vmx(vcpu)->loaded_vmcs->msr_bitmap; + + if (msr <= 0x1fff) { + return !!test_bit(msr, msr_bitmap + 0x800 / f); + } else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff)) { + msr &= 0x1fff; + return !!test_bit(msr, msr_bitmap + 0xc00 / f); + } + + return true; +} + +/* * Check if MSR is intercepted for L01 MSR bitmap. */ static bool msr_write_intercepted_l01(struct kvm_vcpu *vcpu, u32 msr) @@ -2981,6 +3005,13 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) case MSR_IA32_TSC: msr_info->data = guest_read_tsc(vcpu); 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)) @@ -3091,6 +3122,36 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 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)) @@ -5243,6 +5304,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) u64 cr0;
vmx->rmode.vm86_active = 0; + vmx->spec_ctrl = 0;
vmx->soft_vnmi_blocked = 0;
@@ -8828,6 +8890,15 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
vmx_arm_hv_timer(vcpu);
+ /* + * 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 */ @@ -8946,6 +9017,27 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) #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. + * + * For non-nested case: + * If the L01 MSR bitmap does not intercept the MSR, then we need to + * save it. + * + * For nested case: + * If the L02 MSR bitmap does not intercept the MSR, then we need to + * save it. + */ + if (!msr_write_intercepted(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();
@@ -9505,7 +9597,7 @@ static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu, unsigned long *msr_bitmap_l1; unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.vmcs02.msr_bitmap; /* - * pred_cmd is trying to verify two things: + * pred_cmd & spec_ctrl are trying to verify two things: * * 1. L0 gave a permission to L1 to actually passthrough the MSR. This * ensures that we do not accidentally generate an L02 MSR bitmap @@ -9518,9 +9610,10 @@ static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu, * the MSR. */ bool pred_cmd = msr_write_intercepted_l01(vcpu, MSR_IA32_PRED_CMD); + bool spec_ctrl = msr_write_intercepted_l01(vcpu, MSR_IA32_SPEC_CTRL);
if (!nested_cpu_has_virt_x2apic_mode(vmcs12) && - !pred_cmd) + !pred_cmd && !spec_ctrl) return false;
page = nested_get_page(vcpu, vmcs12->msr_bitmap); @@ -9559,6 +9652,12 @@ static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu, } }
+ if (spec_ctrl) + nested_vmx_disable_intercept_for_msr( + msr_bitmap_l1, msr_bitmap_l0, + MSR_IA32_SPEC_CTRL, + MSR_TYPE_R | MSR_TYPE_W); + if (pred_cmd) nested_vmx_disable_intercept_for_msr( msr_bitmap_l1, msr_bitmap_l0, diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 94d1573..75f756e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -975,7 +975,7 @@ 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_TSC_AUX, - MSR_IA32_ARCH_CAPABILITIES + MSR_IA32_SPEC_CTRL, MSR_IA32_ARCH_CAPABILITIES };
static unsigned num_msrs_to_save;