From mboxrd@z Thu Jan  1 00:00:00 1970
From: Toshi Kani <toshi.kani@hpe.com>
Subject: Re: [Xen-devel] MTRR on Xen - BIOS use and implications for Linux
Date: Tue, 29 Mar 2016 16:14:41 -0600
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To: "Luis R. Rodriguez" <mcgrof@kernel.org>, David Vrabel <david.vrabel@citrix.com>, Toshi Kani <toshi.kani@hp.com>
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On Tue, 2016-03-29 at 10:22 -0700, Luis R. Rodriguez wrote:
> On Thu, Mar 17, 2016 at 11:56 AM, Luis R. Rodriguez <mcgrof@kernel.or=
g>
> wrote:
> > On Thu, Mar 17, 2016 at 11:13:03AM +0000, David Vrabel wrote:
> > > On 16/03/16 20:08, Luis R. Rodriguez wrote:
> > > > Toshi noted a while ago as well that if BIOS/firmware enables M=
TRR
> > > > but the kernel does not have it enabled one issue might have be=
en
> > > > any MTRRs set up by the BIOS and ensuring the mapping is respec=
ted,
>=20
> To be clear the requirement expressed here was needing at least to
> implement get_mtrr() on the Linux Xen guest side, it'd call the
> already implemented hypercall XENPF_read_memtype in turn. Toshi had
> hinted this was perhaps needed on the Linux Xen guest side given that
> the BIOS may have set up MTRRs on its own, so we needed the guest to
> be able to get the right type for a particular range. More on that
> below

No, I did not say that. :-) =C2=A0I said it because you mentioned that =
you
wanted to disable MTRRs even though BIOS enabled MTRRs.

My point is that the kernel should not change the MTRR setup. =C2=A0Tha=
t is:
=C2=A0- If BIOS enables MTRRs, then kernel needs to keep them enabled.
=C2=A0- If BIOS disables MTRRs, then the kernel needs to keep them disa=
bled.

Therefore, the kernel can keep MTRRs disabled on Xen guests.

I think you repeated the same questions in this email, so please refer =
my
previous reply for the rest.

Thanks,
-Toshi