linux-kernel - Re: [PATCH] x86, kvm: Add MSR_AMD64_BU

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Message-ID: <20130213153741.GE9817@redhat.com>
Date:	Wed, 13 Feb 2013 17:37:41 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Borislav Petkov <bp@...en8.de>, kvm@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Boris Ostrovsky <boris.ostrovsky@....com>,
	Andre Przywara <andre@...rep.de>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH] x86, kvm: Add MSR_AMD64_BU_CFG2 to the list of ignored
 MSRs

On Wed, Feb 13, 2013 at 02:35:49PM +0100, Borislav Petkov wrote:
> On Wed, Feb 13, 2013 at 02:10:02PM +0200, Gleb Natapov wrote:
> > > > Is your guest compiled without PV support? With PV Linux traps #GP for
> > > > all MSRs and it saves us in more than one places.
> > > 
> > > Yes, CONFIG_PARAVIRT_GUEST is not set on the guest kernel.
> > > 
> > Thanks. It does not mean that the patch should not be applied though.
> 
> Right,
> 
> but, come to think of it, adding an MSR each time to those functions
> could turn out to be a PITA. The PV solution with trapping on the MSR
> accesses might be better so maybe CONFIG_KVM should do
> 
PV solution does not exists for some other guests.

> select KVM_GUEST
> 
> ?
I can easily imaging the situation where one whats to build different
kernels for host and guest and do not have PV in the host one.

> 
> This is even a good forward-looking solution.
> 
> > I cannot seems to find the documentation for the MSR anywhere, do you
> > have a pointer?
> 
> http://support.amd.com/us/Processor_TechDocs/31116.pdf, p.438
> 
Thanks,

--
			Gleb.
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