Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

Liran Alon
2018-02-26T09:26:29Z

----- kernellwp@gmail.com 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>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/x86.c | 8 ++++++--
> 2 files changed, 7 insertions(+), 2 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 1a3ed81..cc51c61 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2247,7 +2247,6 @@ 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:
> @@ -2255,6 +2254,10 @@ 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:
> @@ -2550,7 +2553,7 @@ 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:
> @@ -8232,6 +8235,7 @@ 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);
> }
> --
> 2.7.4

I think you need to add MSR_IA32_UCODE_REV to emulated_msrs[]
to allow for proper live-migration of this MSR value.

The rest seems fine to me. :)

Regards,
-Liran