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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Wed, 4 Sep 2019 09:53:53 +0200
Message-ID: <CAKMK7uH0jxaWJLxfXfGLyN-Rb=0ZKUFTkrEPdFCuGCh4ORCv9w@mail.gmail.com>
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>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        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>,
        "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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On Wed, Sep 4, 2019 at 8:49 AM Thomas Hellstr=C3=B6m (VMware)
<thomas_os@shipmail.org> wrote:
> On 9/4/19 1:15 AM, Andy Lutomirski wrote:
> > But, reading this, I have more questions:
> >
> > Can=E2=80=99t you get rid of cvma by using vmf_insert_pfn_prot()?
>
> It looks like that, although there are comments in the code about
> serious performance problems using VM_PFNMAP / vmf_insert_pfn() with
> write-combining and PAT, so that would require some serious testing with
> hardware I don't have. But I guess there is definitely room for
> improvement here. Ideally we'd like to be able to change the
> vma->vm_page_prot within fault(). But we can

Just a quick comment on this: It's the repeated (per-pfn/pte) lookup
of the PAT tables, which are dead slow. If you have a struct
io_mapping then that can be done once, and then just blindly inserted.
See remap_io_mapping in i915.
-Daniel
--=20
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch