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

[Jan Beulich]

>>> On 18.08.16 at 12:16, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 18/08/16 11:06, Jan Beulich wrote:
>>>>> On 17.08.16 at 22:32, <konrad.wilk@xxxxxxxxxx> 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