linux-kernel - Re: XSA 154 and ISA region (640K -> 1MB) WB cache instead of UC

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Date:   Fri, 19 Aug 2016 09:14:23 -0600
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:     <stefan.bader@...onical.com>, <david.vrabel@...rix.com>,
        "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        <chuck.anderson@...cle.com>, "Juergen Gross" <JGross@...e.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: XSA 154 and ISA region (640K -> 1MB) WB cache instead of
 UC

>>> On 19.08.16 at 16:52, <konrad.wilk@...cle.com> wrote:
> On Thu, Aug 18, 2016 at 04:06:33AM -0600, Jan Beulich wrote:
>> >>> On 17.08.16 at 22:32, <konrad.wilk@...cle.com> wrote:
>> >    Looking at the kernel it assumes that WB is ok for 640KB->1MB.
>> >    The comment says:
>> >    " /* Low ISA region is always mapped WB in page table. No need to track *"
>> 
>> As per above it's not clear to me what this comment is backed by.
> 
> I was hoping you would know :-)
> 
> Ah, commit 2e5d9c857d4e6c9e7b7d8c8c86a68a7842d213d6
> Author: venkatesh.pallipadi@...el.com <venkatesh.pallipadi@...el.com>
> Date:   Tue Mar 18 17:00:14 2008 -0700
> 
>     x86: PAT infrastructure patch
>     
>     Sets up pat_init() infrastructure.
>     
> 
> which sets the MTRR for that region.

Hmm, that's the commit which introduced pat.c years ago. I can't
see it writing an MTRRs though, nor can I see it backing the comment
in adds in any way. I guess I'm confused...

Jan