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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Eduardo Habkost" <ehabkost@redhat.com>,
	"Wanpeng Li" <kernellwp@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version
Date: Mon, 23 Apr 2018 18:03:40 +0200	[thread overview]
Message-ID: <7eeb63dd-5f7f-df91-47b1-7b15005cf45c@redhat.com> (raw)
In-Reply-To: <20180423125849.GD22238@pd.tnic>

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