linux-kernel - Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted

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Date:   Sun, 11 Aug 2019 04:55:27 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Ram Pai <linuxram@...ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        David Gibson <david@...son.dropbear.id.au>,
        Alexey Kardashevskiy <aik@...ux.ibm.com>,
        Paul Mackerras <paulus@...abs.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted

On Sun, Aug 11, 2019 at 07:56:07AM +0200, Christoph Hellwig wrote:
> So we need a flag on the virtio device, exposed by the
> hypervisor (or hardware for hw virtio devices) that says:  hey, I'm real,
> don't take a shortcut.

The point here is that it's actually still not real. So we would still
use a physical address. However Linux decides that it wants extra
security by moving all data through the bounce buffer.  The distinction
made is that one can actually give device a physical address of the
bounce buffer.

-- 
MST