From: Joerg Roedel <jroedel@suse.de>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>,
linux-kernel@vger.kernel.org,
Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cornelia.huck@de.ibm.com>,
Sebastian Ott <sebott@linux.vnet.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Christoph Hellwig <hch@lst.de>,
benh@kernel.crashing.org, KVM <kvm@vger.kernel.org>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
linux-s390 <linux-s390@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH 3/3] virtio_pci: Use the DMA API
Date: Wed, 28 Oct 2015 11:50:47 +0900 [thread overview]
Message-ID: <20151028025047.GF18467@suse.de> (raw)
In-Reply-To: <1445998972.3405.174.camel@infradead.org>
On Wed, Oct 28, 2015 at 11:22:52AM +0900, David Woodhouse wrote:
> On Wed, 2015-10-28 at 11:15 +0900, Joerg Roedel wrote:
> > I think a good test for that is to boot a virtio kvm-guest with
> > swiotlb=force and see if it still works.
>
> That's useful but doesn't cover the cases where dma_wmb() is needed,
> right?
>
> We should make sure we're handling descriptors properly as we would for
> real hardware, and ensuring that addresses etc. are written to the
> descriptor (and a write barrier occurs) *before* the bit is set which
> tells the 'hardware' that it owns that descriptor.
Hmm, good question. The virtio code has virtio_rmb/wmb and should
already call it in the right places.
The virtio-barriers default to rmb()/wmb() unless weak_barriers is set,
in which case it calls dma_rmb()/wmb(), just a compiler barrier on x86.
And weak_barriers is set by the virtio drivers when creating the queue,
and the drivers should know what they are doing. Saying this, I think
the virtio-drivers should already get this right.
Joerg
next prev parent reply other threads:[~2015-10-28 2:51 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-28 1:17 [PATCH 0/3] virtio DMA API core stuff Andy Lutomirski
2015-10-28 1:17 ` [PATCH 1/3] virtio_net: Stop doing DMA from the stack Andy Lutomirski
2015-10-28 2:07 ` Joerg Roedel
2015-10-28 2:14 ` Andy Lutomirski
2015-10-28 1:17 ` [PATCH 2/3] virtio_ring: Support DMA APIs Andy Lutomirski
2015-10-28 2:06 ` Joerg Roedel
2015-10-28 2:13 ` Andy Lutomirski
2015-10-28 2:21 ` Joerg Roedel
2015-10-28 5:12 ` Andy Lutomirski
2015-10-28 2:27 ` Christian Borntraeger
2015-10-28 5:09 ` Andy Lutomirski
2015-10-28 1:17 ` [PATCH 3/3] virtio_pci: Use the DMA API Andy Lutomirski
2015-10-28 2:15 ` Joerg Roedel
2015-10-28 2:22 ` David Woodhouse
2015-10-28 2:50 ` Joerg Roedel [this message]
2015-10-28 2:25 ` Joerg Roedel
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