linux-kernel - Re: [PATCH v2 1/4] x86/mm: Export force_dma

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Date:   Tue, 3 Sep 2019 09:22:04 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        dri-devel@...ts.freedesktop.org, pv-drivers@...are.com,
        linux-graphics-maintainer@...are.com, linux-kernel@...r.kernel.org,
        Thomas Hellstrom <thellstrom@...are.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v2 1/4] x86/mm: Export force_dma_unencrypted

On Tue, Sep 03, 2019 at 04:32:45PM +0200, Thomas Hellström (VMware) wrote:
> Is this a layer violation concern, that is, would you be ok with a similar
> helper for TTM, or is it that you want to force the graphics drivers into
> adhering strictly to the DMA api, even when it from an engineering
> perspective makes no sense?

>From looking at DRM I strongly believe that making DRM use the DMA
mapping properly makes a lot of sense from the engineering perspective,
and this series is a good argument for that positions.  If DRM was using
the DMA properl we would not need this series to start with, all the
SEV handling is hidden behind the DMA API.  While we had occasional
bugs in that support fixing it meant that it covered all drivers
properly using that API.