Re: [RFC PATCH v3 02/20] x86: Set the write-protect cache mode for full PAT support

[Kani, Toshimitsu]

On Thu, 2016-11-10 at 14:14 +0100, Borislav Petkov wrote:
> + Toshi.
> 
> On Wed, Nov 09, 2016 at 06:34:48PM -0600, Tom Lendacky wrote:
> > 
> > For processors that support PAT, set the write-protect cache mode
> > (_PAGE_CACHE_MODE_WP) entry to the actual write-protect value
> > (x05).

Using slot 6 may be more cautious (for the same reason slot 7 was used
for WT), but I do not have a strong opinion for it.

set_page_memtype() cannot track the use of WP type since there is no
extra-bit available for WP, but WP is only supported by
early_memremap_xx() interfaces in this series. ÂSo, I think we should
just document that WP is only intended for temporary mappings at boot-
time until this issue is resolved. ÂAlso, we need to make sure that
this early_memremap for WP is only called after pat_init() is done.

A nit - please add WP to the function header comment below.
"This function initializes PAT MSR and PAT table with an OS-defined
value to enable additional cache attributes, WC and WT."

Thanks,
-Toshi