linux-kernel - Re: [RFC 0/4] Virtio uses DMA API for all devices

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Date:   Mon, 6 Aug 2018 23:12:13 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        aik@...abs.ru, robh@...nel.org, joe@...ches.com,
        elfring@...rs.sourceforge.net, david@...son.dropbear.id.au,
        jasowang@...hat.com, mpe@...erman.id.au, linuxram@...ibm.com,
        haren@...ux.vnet.ibm.com, paulus@...ba.org,
        srikar@...ux.vnet.ibm.com, robin.murphy@....com,
        jean-philippe.brucker@....com, marc.zyngier@....com
Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices

On Mon, Aug 06, 2018 at 11:35:39PM +0300, Michael S. Tsirkin wrote:
> > As I said replying to Christoph, we are "leaking" into the interface
> > something here that is really what's the VM is doing to itself, which
> > is to stash its memory away in an inaccessible place.
> > 
> > Cheers,
> > Ben.
> 
> I think Christoph merely objects to the specific implementation.  If
> instead you do something like tweak dev->bus_dma_mask for the virtio
> device I think he won't object.

As long as we also document how dev->bus_dma_mask is tweaked for this
particular virtual bus, yes.