From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [Xen-devel] MTRR on Xen - BIOS use and implications for Linux
Date: Thu, 17 Mar 2016 11:13:03 +0000
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To: "Luis R. Rodriguez" <mcgrof@kernel.org>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Keir Fraser <keir@xen.org>
Cc: Juergen Gross <jgross@suse.com>, X86 ML <x86@kernel.org>, Toshi Kani <toshi.kani@hp.com>, 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>
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tl;dr?

Somewhere in here are some actual questions which I will attempt to
answer. Please try and be more concise in future.

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, in
> particular UC settings, this concern is raised above. Another issue
> though is that the kernel would be "unable to verify if a large page
> mapping is aligned with MTRRs" [3]

This is not a relevant concern for Xen guests:   PV guests do not
support superpage mappings and HVM guests never see real MTRRs.

David