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Subject: Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD
 memory encryption
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28VMware=29?= 
        <thomas_os@shipmail.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
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        VMware Graphics <linux-graphics-maintainer@vmware.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <6d0fafcc-b596-481b-7b22-1f26f0c02c5c@intel.com>
Date:   Tue, 3 Sep 2019 12:55:29 -0700
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On 9/3/19 12:51 PM, Daniel Vetter wrote:
>> The thing we need to stop is having mixed encryption rules under one VMA.
> The point here is that we want this. We need to be able to move the
> buffer between device ptes and system memory ptes, transparently,
> behind userspace back, without races. And the fast path (which is "no
> pte exists for this vma") must be real fast, so taking mmap_sem and
> replacing the vma is no-go.

So, when the user asks for encryption and we say, "sure, we'll encrypt
that", then we want the device driver to be able to transparently undo
that encryption under the covers for device memory?  That seems suboptimal.

I'd rather the device driver just say: "Nope, you can't encrypt my VMA".
 Because that's the truth.