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SubjectRe: [PATCH v4] KVM: X86: Allow userspace to define the microcode version
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On 27/02/2018 03:35, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Linux (among the others) has checks to make sure that certain features
> aren't enabled on a certain family/model/stepping if the microcode version
> isn't greater than or equal to a known good version.
>
> By exposing the real microcode version, we're preventing buggy guests that
> don't check that they are running virtualized (i.e., they should trust the
> hypervisor) from disabling features that are effectively not buggy.
>
> Suggested-by: Filippo Sironi <sironi@amazon.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Liran Alon <liran.alon@oracle.com>
> Cc: Nadav Amit <nadav.amit@gmail.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v3 -> v4:
> * add the shifts back

Please wait for a review instead of pushing new versions continuously.
Leaving the shifts means that MSR_IA32_UCODE_REV's bits 0-31 are zeroed
even if KVM_SET_MSRS makes them nonzero.

Paolo

> v2 -> v3:
> * remove the shifts
> * add the MSR_IA32_UCODE_REV version to the "feature MSRs"
> v1 -> v2:
> * add MSR_IA32_UCODE_REV to emulated_msrs
>
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/x86.c | 19 +++++++++++++++----
> 2 files changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 938d453..6e13f2f 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -507,6 +507,7 @@ struct kvm_vcpu_arch {
> u64 smi_count;
> bool tpr_access_reporting;
> u64 ia32_xss;
> + u32 microcode_version;
>
> /*
> * Paging state of the vcpu
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d4985a9..0299b6e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1058,6 +1058,7 @@ static unsigned num_emulated_msrs;
> static u32 msr_based_features[] = {
> MSR_IA32_ARCH_CAPABILITIES,
> MSR_F10H_DECFG,
> + MSR_IA32_UCODE_REV,
> };
>
> static unsigned int num_msr_based_features;
> @@ -1067,8 +1068,14 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
> struct kvm_msr_entry msr;
>
> msr.index = index;
> - if (kvm_x86_ops->get_msr_feature(&msr))
> - return 1;
> + switch (msr.index) {
> + case MSR_IA32_UCODE_REV:
> + rdmsrl(msr.index, msr.data);
> + break;
> + default:
> + if (kvm_x86_ops->get_msr_feature(&msr))
> + return 1;
> + }
>
> *data = msr.data;
>
> @@ -2248,7 +2255,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>
> switch (msr) {
> case MSR_AMD64_NB_CFG:
> - case MSR_IA32_UCODE_REV:
> case MSR_IA32_UCODE_WRITE:
> case MSR_VM_HSAVE_PA:
> case MSR_AMD64_PATCH_LOADER:
> @@ -2256,6 +2262,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> case MSR_AMD64_DC_CFG:
> break;
>
> + case MSR_IA32_UCODE_REV:
> + if (msr_info->host_initiated)
> + vcpu->arch.microcode_version = data >> 32;
> + break;
> case MSR_EFER:
> return set_efer(vcpu, data);
> case MSR_K7_HWCR:
> @@ -2551,7 +2561,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> msr_info->data = 0;
> break;
> case MSR_IA32_UCODE_REV:
> - msr_info->data = 0x100000000ULL;
> + msr_info->data = (u64)vcpu->arch.microcode_version << 32;
> break;
> case MSR_MTRRcap:
> case 0x200 ... 0x2ff:
> @@ -8233,6 +8243,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> vcpu->arch.regs_dirty = ~0;
>
> vcpu->arch.ia32_xss = 0;
> + vcpu->arch.microcode_version = 0x1;
>
> kvm_x86_ops->vcpu_reset(vcpu, init_event);
> }
>

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