linux-kernel - Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD memory encryption

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Message-ID: <CAKMK7uH0jxaWJLxfXfGLyN-Rb=0ZKUFTkrEPdFCuGCh4ORCv9w@mail.gmail.com>
Date:   Wed, 4 Sep 2019 09:53:53 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        pv-drivers@...are.com,
        VMware Graphics <linux-graphics-maintainer@...are.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD
 memory encryption

On Wed, Sep 4, 2019 at 8:49 AM Thomas Hellström (VMware)
<thomas_os@...pmail.org> wrote:
> On 9/4/19 1:15 AM, Andy Lutomirski wrote:
> > But, reading this, I have more questions:
> >
> > Can’t 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
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch