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

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Date:	Wed, 27 Apr 2016 08:12:56 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Tom Lendacky <thomas.lendacky@....com>
Cc:	linux-arch <linux-arch@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kasan-dev <kasan-dev@...glegroups.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	iommu@...ts.linux-foundation.org,
	Radim Krčmář <rkrcmar@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Joerg Roedel <joro@...tes.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Alexander Potapenko <glider@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v1 01/18] x86: Set the write-protect cache mode for
 AMD processors

On Wed, Apr 27, 2016 at 8:05 AM, Tom Lendacky <thomas.lendacky@....com> wrote:
> On 04/27/2016 09:47 AM, Andy Lutomirski wrote:
>> On Wed, Apr 27, 2016 at 7:44 AM, Tom Lendacky <thomas.lendacky@....com> wrote:
>>> On 04/27/2016 09:33 AM, Andy Lutomirski wrote:
>>>> On Tue, Apr 26, 2016 at 3:56 PM, Tom Lendacky <thomas.lendacky@....com> 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