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From: Toshi Kani <toshi.kani@hpe.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	David Vrabel <david.vrabel@citrix.com>,
	Toshi Kani <toshi.kani@hp.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	Keir Fraser <keir@xen.org>, Juergen Gross <jgross@suse.com>,
	X86 ML <x86@kernel.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Stuart Hayes <stuart.w.hayes@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Yinghai Lu <yinghai@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Prarit Bhargava <prarit@redhat.com>
Subject: Re: [Xen-devel] MTRR on Xen - BIOS use and implications for Linux
Date: Tue, 29 Mar 2016 16:14:41 -0600	[thread overview]
Message-ID: <1459289681.6393.714.camel@hpe.com> (raw)
In-Reply-To: <CAB=NE6WiTg00iyMvebj0OcCR+jBjD-e-Fg2AhWsvHG=YayLP_Q@mail.gmail.com>

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.org>
> 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 MTRR
> > > > but the kernel does not have it enabled one issue might have been
> > > > any MTRRs set up by the BIOS and ensuring the mapping is respected,
> 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. :-)  I 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.  That is:
 - If BIOS enables MTRRs, then kernel needs to keep them enabled.
 - If BIOS disables MTRRs, then the kernel needs to keep them disabled.

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.


  reply	other threads:[~2016-03-29 22:14 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-16 20:08 MTRR on Xen - BIOS use and implications for Linux Luis R. Rodriguez
2016-03-17 11:13 ` [Xen-devel] " David Vrabel
2016-03-17 18:56   ` Luis R. Rodriguez
2016-03-29 17:22     ` Luis R. Rodriguez
2016-03-29 22:14       ` Toshi Kani [this message]
2016-03-29 22:28         ` Luis R. Rodriguez

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