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

[Tom Lendacky]

On 11/10/2016 07:26 PM, Kani, Toshimitsu wrote:
> 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.  So, I think we should
> just document that WP is only intended for temporary mappings at boot-
> time until this issue is resolved.  Also, we need to make sure that
> this early_memremap for WP is only called after pat_init() is done.

Sounds good, I'll add documentation to cover these points.

> 
> 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."

Will do.

Thanks,
Tom

> 
> Thanks,
> -Toshi
> 
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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.  So, I think we should
just document that WP is only intended for temporary mappings at boot-
time until this issue is resolved.  Also, 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
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Re: [RFC PATCH v3 02/20] x86: Set the write-protect cache mode for full PAT support

[Borislav Petkov]

+ 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).
> 
> Acked-by: Borislav Petkov 
> Signed-off-by: Tom Lendacky 
> ---
>  arch/x86/mm/pat.c |4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 170cc4f..87e8952 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -355,7 +355,7 @@ void pat_init(void)
>*  0102UC-: _PAGE_CACHE_MODE_UC_MINUS
>*  0113UC : _PAGE_CACHE_MODE_UC
>*  1004WB : Reserved
> -  *  1015WC : Reserved
> +  *  1015WP : _PAGE_CACHE_MODE_WP
>*  1106UC-: Reserved
>*  1117WT : _PAGE_CACHE_MODE_WT
>*
> @@ -363,7 +363,7 @@ void pat_init(void)
>* corresponding types in the presence of PAT errata.
>*/
>   pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
> -   PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, WT);
> +   PAT(4, WB) | PAT(5, WP) | PAT(6, UC_MINUS) | PAT(7, WT);
>   }
>  
>   if (!boot_cpu_done) {
> 
> 

-- 
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.
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