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Subject: Re: [RFC PATCH 1/2] x86: Don't let pgprot_modify() change the page encryption bit
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <20190905152438.GA18286@infradead.org>
Date:   Tue, 10 Sep 2019 09:11:24 -0700
Cc:     =?utf-8?Q? "Thomas_Hellstr=C3=B6m_=28VMware=29" ?= 
        <thomas_os@shipmail.org>, Dave Hansen <dave.hansen@intel.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        pv-drivers@vmware.com, Thomas Hellstrom <thellstrom@vmware.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        =?utf-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
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References: <20190905103541.4161-1-thomas_os@shipmail.org> <20190905103541.4161-2-thomas_os@shipmail.org> <608bbec6-448e-f9d5-b29a-1984225eb078@intel.com> <b84d1dca-4542-a491-e585-a96c9d178466@shipmail.org> <20190905152438.GA18286@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Sep 5, 2019, at 8:24 AM, Christoph Hellwig <hch@infradead.org> wrote:
>=20
>> On Thu, Sep 05, 2019 at 05:21:24PM +0200, Thomas Hellstr=C3=B6m (VMware) w=
rote:
>>> On 9/5/19 4:15 PM, Dave Hansen wrote:
>>> Hi Thomas,
>>>=20
>>> Thanks for the second batch of patches!  These look much improved on all=

>>> fronts.
>>=20
>> Yes, although the TTM functionality isn't in yet. Hopefully we won't have=
 to
>> bother you with those though, since this assumes TTM will be using the dm=
a
>> API.
>=20
> Please take a look at dma_mmap_prepare and dma_mmap_fault in this
> branch:
>=20
>    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-mma=
p-improvements
>=20
> they should allow to fault dma api pages in the page fault handler.  But
> this is totally hot off the press and not actually tested for the last
> few patches.  Note that I've also included your two patches from this
> series to handle SEV.

I read that patch, and it seems like you=E2=80=99ve built in the assumption t=
hat all pages in the mapping use identical protection or, if not, that the s=
ame fake vma hack that TTM already has is used to fudge around it.  Could it=
 be reworked slightly to avoid this?

I wonder if it=E2=80=99s a mistake to put the encryption bits in vm_page_pro=
t at all.=