Re: [Xen-devel] Xen hypervisor hangs on booting against c/s 16925

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 29.01.08 11:45 >>>
>On 29/1/08 10:34, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> Otoh, with
>> PAGE_HYPERVISOR_NOCACHE encoding UC- rather than UC, mapping
>> WP MTRR regions this way would yield (model specific) WC, which again
>> seems suspicious, so maybe the VGA hole should simply be kept (from
>> boot, at UC-), but everything else should be forced to UC (or MTRRs
>> should be inquired so that at least WP regions can be kept WP).
>
>If we don't write to a MTRR WP region, then actually mapping as WC does not
>matter. We never write to the range 0xc0000-0xfffff. Anything we write to
>below 0xa0000 had better be RAM, or we've got bigger problems than the WP
>attribute!

Unfortunately it does matter - WC does not permit read caching, but
does permit speculative reads. That's both not what we want.

Jan


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