From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH v2] KVM: SVM: Sync g_pat with guest-written PAT value
Date: Tue, 21 Apr 2015 14:21:49 +0200
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Cc: Jan Kiszka <jan.kiszka@siemens.com>, kvm <kvm@vger.kernel.org>,
	Joel Schopp <joel.schopp@amd.com>
To: Paolo Bonzini <pbonzini@redhat.com>
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2015-04-21 13:09+0200, Paolo Bonzini:
> 
> 
> On 20/04/2015 19:25, Jan Kiszka wrote:
> > When hardware supports the g_pat VMCB field, we can use it for emulating
> > the PAT configuration that the guest configures by writing to the
> > corresponding MSR.
> > 
> > Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> 
> I'm not sure about this.  The problem is that, unlike Intel, AMD has no
> way for the host to force its PAT value and ignore the guest's.  I'm
> worried about potential performance problems in the guest.

We already set g_pat to 0x0007040600070406ULL in init_vmcb().
This patch uses caching that the guest expects, which might improve
performance as well.  I think it's a step in right direction even if we
somehow optimize cache coherent cases later.