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Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version
To: Eduardo Habkost <ehabkost@redhat.com>,
        Wanpeng Li <kernellwp@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>, LKML <linux-kernel@vger.kernel.org>,
        kvm <kvm@vger.kernel.org>,
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Wed, 18 Apr 2018 12:36:37 +0200
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On 18/04/2018 11:03, Eduardo Habkost wrote:
>>> QEMU setting ucode_rev automatically using the host value when
>>> using "-cpu host" (with no need for explicit ucode_rev option)
>>> makes sense to me.
>> QEMU can't get the host value by rdmsr MSR_IA32_UCODE_REV directly
>> since rdmsr will #GP when ring !=0, any idea?
> By looking at kvm_get_msr_feature(), it looks like
> ioctl(system_fd, KVM_GET_MSRS) would return the host MSR value
> for us.

Yes, that's exactly what it was introduced for (together with other MSRs
including VMX capabilities).

Paolo