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

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Date:   Wed, 18 Apr 2018 12:36:37 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Eduardo Habkost <ehabkost@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

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