Messages in this thread |  | | Subject | Re: [PATCH v3 2/4] KVM: x86: Add IBPB support | From | David Woodhouse <> | Date | Tue, 30 Jan 2018 14:36:18 +0000 |
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On Tue, 2018-01-30 at 08:22 -0600, Tom Lendacky wrote: > > @@ -918,6 +919,9 @@ static void svm_vcpu_init_msrpm(u32 *msrpm) > > > > set_msr_interception(msrpm, direct_access_msrs[i].index, 1, 1); > > } > > + > > + if (boot_cpu_has(X86_FEATURE_IBPB)) > > + set_msr_interception(msrpm, MSR_IA32_PRED_CMD, 1, 1); > > Not sure you really need the check here. If the feature isn't available > in the hardware, then it won't be advertised in the CPUID bits to the > guest, so the guest shouldn't try to write to the msr. If it does, it > will #GP. So I would think it could be set all the time to not be > intercepted, no?
The check for boot_cpu_has() is wrong and is fairly redundant as you say. What we actually want is guest_cpu_has(). We *don't* want to pass the MSR through for a recalcitrant guest to bash on, if we have elected not to expose this feature to the guest.
On Intel right now it's *really* important that we don't allow it to be touched, even if a write would succeed. So even boot_cpu_has() would not be entirely meaningless there. :)
> > @@ -3330,6 +3331,14 @@ 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_PRED_CMD: > > + if (!msr_info->host_initiated && > > + !guest_cpuid_has(vcpu, X86_FEATURE_IBPB)) > > + return 1; > > + > > + if (data & PRED_CMD_IBPB) > > + wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB); > > + break; > > Should this also be in svm.c or as common code in x86.c?
See my response to [0/4]. I suggested that, but noted that it wasn't entirely clear where we'd put the storage for SPEC_CTRL. We probably *could* manage it for IBPB though.
> > > > case MSR_IA32_CR_PAT: > > if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) { > > if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data)) > > @@ -9548,6 +9557,9 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id) > > goto free_msrs; > > > > msr_bitmap = vmx->vmcs01.msr_bitmap; > > + > > + if (boot_cpu_has(X86_FEATURE_IBPB)) > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PRED_CMD, MSR_TYPE_W); > > Same comment here as in svm.c, is the feature check necessary?
Again, yes but it should be guest_cpu_has() and we couldn't see how :) [unhandled content-type:application/x-pkcs7-signature] |  |