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Date:   Mon, 12 Aug 2019 14:13:24 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ram Pai <linuxram@us.ibm.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        virtualization@lists.linux-foundation.org,
        linuxppc-devel@lists.ozlabs.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Jason Wang <jasowang@redhat.com>,
        David Gibson <david@gibson.dropbear.id.au>,
        Alexey Kardashevskiy <aik@linux.ibm.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is
 encrypted
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On Sat, Aug 10, 2019 at 11:46:21PM -0700, Ram Pai wrote:
> If the hypervisor (hardware for hw virtio devices) does not mandate a
> DMA API, why is it illegal for the driver to request, special handling
> of its i/o buffers? Why are we associating this special handling to
> always mean, some DMA address translation? Can't there be 
> any other kind of special handling needs, that has nothing to do with
> DMA address translation?

I don't think it is illegal per se.  It is however completely broken
if we do that decision on a system weide scale rather than properly
requesting it through a per-device flag in the normal virtio framework.