From: "Michael S. Tsirkin" <mst@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: jasowang@redhat.com, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
iommu@lists.linux-foundation.org, eric.auger.pro@gmail.com,
robin.murphy@arm.com
Subject: Re: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call
Date: Tue, 23 Jul 2019 11:47:27 -0400 [thread overview]
Message-ID: <20190723114504-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20190723153830.GD720@lst.de>
On Tue, Jul 23, 2019 at 05:38:30PM +0200, Christoph Hellwig wrote:
> On Mon, Jul 22, 2019 at 11:33:35AM -0400, Michael S. Tsirkin wrote:
> > On Mon, Jul 22, 2019 at 04:55:09PM +0200, Eric Auger wrote:
> > > Do not call dma_max_mapping_size for devices that have no DMA
> > > mask set, otherwise we can hit a NULL pointer dereference.
> > >
> > > This occurs when a virtio-blk-pci device is protected with
> > > a virtual IOMMU.
> > >
> > > Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> > > Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > > Suggested-by: Christoph Hellwig <hch@lst.de>
> >
> > Christoph, I wonder why did you suggest this?
> > The connection between dma_mask and dma_max_mapping_size
> > is far from obvious. The documentation doesn't exist.
> > Do we really have to teach all users about this hack?
> > Why not just make dma_max_mapping_size DTRT?
>
> Because we should not call into dma API functions for devices that
> are not DMA capable.
I'd rather call is_device_dma_capable then, better than poking
at DMA internals.
--
MST
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next prev parent reply other threads:[~2019-07-23 15:47 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-22 14:55 [PATCH 0/2] Fix NULL pointer dereference with virtio-blk-pci and virtual IOMMU Eric Auger
2019-07-22 14:55 ` [PATCH 1/2] dma-mapping: Protect dma_addressing_limited against NULL dma_mask Eric Auger
2019-07-22 15:26 ` Christoph Hellwig
2019-07-22 15:46 ` Auger Eric
2019-07-22 14:55 ` [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call Eric Auger
2019-07-22 15:27 ` Christoph Hellwig
2019-07-22 15:39 ` Michael S. Tsirkin
2019-07-22 15:33 ` Michael S. Tsirkin
2019-07-23 15:38 ` Christoph Hellwig
2019-07-23 15:47 ` Michael S. Tsirkin [this message]
2019-07-22 15:36 ` Robin Murphy
2019-07-22 15:45 ` Michael S. Tsirkin
2019-07-23 15:38 ` Christoph Hellwig
2019-07-24 22:10 ` Michael S. Tsirkin
2019-07-25 5:25 ` Christoph Hellwig
2019-07-25 11:53 ` Auger Eric
2019-07-25 13:04 ` Christoph Hellwig
2019-07-25 16:32 ` Auger Eric
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