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Subject: Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD
 memory encryption
To:     =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28VMware=29?= 
        <thomas_os@shipmail.org>, Daniel Vetter <daniel@ffwll.ch>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>, pv-drivers@vmware.com,
        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: <7fa3b178-b9b4-2df9-1eee-54e24d48342e@intel.com>
Date:   Tue, 3 Sep 2019 13:51:28 -0700
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On 9/3/19 1:36 PM, Thomas Hellström (VMware) wrote:
> So the question here should really be, can we determine already at mmap
> time whether backing memory will be unencrypted and adjust the *real*
> vma->vm_page_prot under the mmap_sem?
> 
> Possibly, but that requires populating the buffer with memory at mmap
> time rather than at first fault time.

I'm not connecting the dots.

vma->vm_page_prot is used to create a VMA's PTEs regardless of if they
are created at mmap() or fault time.  If we establish a good
vma->vm_page_prot, can't we just use it forever for demand faults?

Or, are you concerned that if an attempt is made to demand-fault page
that's incompatible with vma->vm_page_prot that we have to SEGV?

> And it still requires knowledge whether the device DMA is always
> unencrypted (or if SEV is active).

I may be getting mixed up on MKTME (the Intel memory encryption) and
SEV.  Is SEV supported on all memory types?  Page cache, hugetlbfs,
anonymous?  Or just anonymous?