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Date:   Mon, 6 Aug 2018 23:32:01 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christoph Hellwig <hch@infradead.org>,
        Will Deacon <will.deacon@arm.com>,
        Anshuman Khandual <khandual@linux.vnet.ibm.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        aik@ozlabs.ru, robh@kernel.org, joe@perches.com,
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        srikar@linux.vnet.ibm.com, robin.murphy@arm.com,
        jean-philippe.brucker@arm.com, marc.zyngier@arm.com
Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices
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On Tue, Aug 07, 2018 at 02:45:25AM +0300, Michael S. Tsirkin wrote:
> > > I think that's where Christoph might have specific ideas about it.
> > 
> > OK well, assuming Christoph can solve the direct case in a way that
> > also work for the virtio !iommu case, we still want some bit of logic
> > somewhere that will "switch" to swiotlb based ops if the DMA mask is
> > limited.
> > 
> > You mentioned an RFC for that ? Do you happen to have a link ?
> 
> No but Christoph did I think.

Do you mean the direct map retpoline mitigation?  It is here:

https://www.spinics.net/lists/netdev/msg495413.html

https://www.spinics.net/lists/netdev/msg495785.html