linux-kernel - Re: [PATCH] x86/kernel/cpu/amd.c: don't apply the lahf

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Message-ID: <alpine.LRH.2.02.1707122220530.9089@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Wed, 12 Jul 2017 22:27:44 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/kernel/cpu/amd.c: don't apply the lahf_lm workaround
 in a hypervisor



On Wed, 12 Jul 2017, Borislav Petkov wrote:

> On Wed, Jul 12, 2017 at 03:19:56AM -0400, Mikulas Patocka wrote:
> > When I start a virtual machine, kvm complains about accesses to an unknown
> > MSR ("vcpu0 unhandled rdmsr: 0xc001100d"). This is caused by the code in
> > init_amd_k8 that tries to work around a BIOS bug that incorrectly sets
> > lahf_lm.
> 
> No need - there are a lot of qemu configurations which cause the
> unhandled MSR warning so no need to pollute the kernel unnecessarily.
> The warning is harmless at that.

It is not strictly needed, but it is annoying. I work in the console and 
it is annoying to see these "unhandled rdmsr" messages printed over the 
screen every time I reboot a virtual machine.

Or do you thnik that the code that prints this warning should be removed 
from the kernel instead?

Mikulas

> -- 
> Regards/Gruss,
>     Boris.
> 
> ECO tip #101: Trim your mails when you reply.
> --