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

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Date:   Mon, 23 Apr 2018 18:03:40 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Eduardo Habkost <ehabkost@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>,
        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 23/04/2018 14:58, Borislav Petkov wrote:
>>>> 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).
> Can't qemu do:
> 
> grep microcode /proc/cpuinfo | awk '{ print $3 }' | head -n 1
> 
> ?

Yes, but you took that a statement bit too narrowly.

We didn't include KVM_GET_MSRS because microcode version wasn't
otherwise available; rather, there's a general need for KVM userspace to
know the values of host MSRs, and microcode is an example.

Paolo