Re: [Xen-devel] [PATCH RFC 0/3] x86: Full support of PAT

[Jan Beulich]

>>> One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> 08/20/14 2:08 PM >>>
>> The Linux kernel currently supports only 4 different cache modes. The PAT MSR
>> is set up in a way that the setting of _PAGE_PAT in a pte doesn't matter: the
>> top 4 entries in the PAT MSR are the same as the 4 lower entries.
>> 
>> This results in the kernel not supporting e.g. write-through mode. Especially
>> this cache mode would speed up drivers of video cards which now have to use
>> uncached accesses.
>
>Pentium II erratum A52 (and similar on quite a few other processors)

But you're aware that for the last two major releases Xen hasn't been supporting
32-bit CPUs at all anymore? I.e. why should we limit functionality under Xen
based on errata on 64-bit-incapable CPUs?

Jan

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