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Re: [Xen-devel] XSA 154 and ISA region (640K -> 1MB) WB cache instead of UC

From "Jan Beulich" <JBeulich@suse.com>
Newsgroups linux.kernel
Subject Re: [Xen-devel] XSA 154 and ISA region (640K -> 1MB) WB cache instead of UC
Date 2016-08-18 13:20 +0200
Message-ID <s7twB-7tk-25@gated-at.bofh.it> (permalink)
References <s7fMZ-62b-3@gated-at.bofh.it> <s7sqR-6Jo-3@gated-at.bofh.it> <s7sAy-6Nh-29@gated-at.bofh.it>
Organization linux.* mail to news gateway

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>>> On 18.08.16 at 12:16, <andrew.cooper3@citrix.com> wrote:
> On 18/08/16 11:06, Jan Beulich wrote:
>>>>> On 17.08.16 at 22:32, <konrad.wilk@oracle.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.
> 
> This states what is in the pagetables.  Not the combined result with MTRRs.
> 
> WB in the pagetables and WC/UB in the MTRRs is a legal combination which
> functions correctly.

True, but then again - haven't I been told multiple times that Linux
nowadays prefers to run without using MTRRs?

Jan

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Thread

XSA 154 and ISA region (640K -> 1MB) WB cache instead of UC Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2016-08-17 22:40 +0200
  Re: XSA 154 and ISA region (640K -> 1MB) WB cache instead of  UC "Jan Beulich" <JBeulich@suse.com> - 2016-08-18 12:10 +0200
    Re: [Xen-devel] XSA 154 and ISA region (640K -> 1MB) WB cache instead  of UC Andrew Cooper <andrew.cooper3@citrix.com> - 2016-08-18 12:20 +0200
      Re: [Xen-devel] XSA 154 and ISA region (640K -> 1MB) WB cache  instead of UC "Jan Beulich" <JBeulich@suse.com> - 2016-08-18 13:20 +0200
        Re: [Xen-devel] XSA 154 and ISA region (640K -> 1MB) WB cache  instead of UC One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-08-19 04:40 +0200
          Re: [Xen-devel] XSA 154 and ISA region (640K -> 1MB) WB cache  instead of UC Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2016-08-19 17:30 +0200
    Re: XSA 154 and ISA region (640K -> 1MB) WB cache instead of UC Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2016-08-19 17:00 +0200
      Re: XSA 154 and ISA region (640K -> 1MB) WB cache instead of  UC "Jan Beulich" <JBeulich@suse.com> - 2016-08-19 17:20 +0200

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