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

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Message-ID: <20180423130823.GM29865@localhost.localdomain>
Date:   Mon, 23 Apr 2018 10:08:23 -0300
From:   Eduardo Habkost <ehabkost@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Paolo Bonzini <pbonzini@...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 Mon, Apr 23, 2018 at 02:58:49PM +0200, Borislav Petkov wrote:
> On Wed, Apr 18, 2018 at 12:36:37PM +0200, Paolo Bonzini wrote:
> > 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).
> 
> Can't qemu do:
> 
> grep microcode /proc/cpuinfo | awk '{ print $3 }' | head -n 1

It could, but why would QEMU do it if a real API already exists
for that?

-- 
Eduardo