Re: [RFC PATCH v1 01/18] x86: Set the write-protect cache mode for AMD processors

[Andy Lutomirski]

On Wed, Apr 27, 2016 at 8:05 AM, Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
> On 04/27/2016 09:47 AM, Andy Lutomirski wrote:
>> On Wed, Apr 27, 2016 at 7:44 AM, Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
>>> On 04/27/2016 09:33 AM, Andy Lutomirski wrote:
>>>> On Tue, Apr 26, 2016 at 3:56 PM, Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
>>>>> For AMD processors that support PAT, set the write-protect cache mode
>>>>> (_PAGE_CACHE_MODE_WP) entry to the actual write-protect value (x05).
>>>>
>>>> What's the purpose of using the WP memory type?
>>>
>>> The WP memory type is used for encrypting or decrypting data "in place".
>>> The use of the WP on the source data will prevent any of the source
>>> data from being cached.  Refer to section 7.10.8 "Encrypt-in-Place" in
>>> the AMD64 APM link provided in the cover letter.
>>>
>>> This memory type will be used in subsequent patches for this purpose.
>>
>> OK.
>>
>> Why AMD-only?  I thought Intel supported WP, too.
>
> Just me being conservative. If there aren't any objections from the
> Intel folks about it we can remove the vendor check and just set it.

I think there are some errata that will cause high PAT references to
incorrectly reference the low parts of the table, but I don't recall
any that go the other way around.  So merely setting WP in a high
entry should be harmless unless something tries to use it.

>
> Thanks,
> Tom
>
>>
>> --Andy
>>



-- 
Andy Lutomirski
AMA Capital Management, LLC