From: Christoph Hellwig <hch@lst.de>
To: Joerg Roedel <joro@8bytes.org>
Cc: Christoph Hellwig <hch@lst.de>,
"Michael S . Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Jens Axboe <axboe@kernel.dk>,
virtualization@lists.linux-foundation.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
iommu@lists.linux-foundation.org, jfehlig@suse.com,
jon.grimm@amd.com, brijesh.singh@amd.com, jroedel@suse.de
Subject: Re: [PATCH 2/3] dma: Introduce dma_max_mapping_size()
Date: Tue, 15 Jan 2019 18:54:18 +0100 [thread overview]
Message-ID: <20190115175418.GA11402@lst.de> (raw)
In-Reply-To: <20190115162322.GA4681@8bytes.org>
On Tue, Jan 15, 2019 at 05:23:22PM +0100, Joerg Roedel wrote:
> Right, I thought about that too, but didn't find a generic way to check
> for all the cases. There are various checks that could be done:
>
> 1) Check if SWIOTLB is initialized at all, if not, return
> SIZE_MAX as the limit. This can't be checked from dma-direct
> code right now, but could be easily implemented.
Yes, this is the low hanging fruit.
> 2) Check for swiotlb=force needs to be done.
>
> 3) Check whether the device can access all of available RAM. I
> have no idea how to check that in an architecture independent
> way. It also has to take memory hotplug into account as well
> as the DMA mask of the device.
>
> An easy approximation could be to omit the limit if the
> dma-mask covers all of the physical address bits available
> on the platform. It would require to pass the dma-mask as an
> additional parameter like it is done in dma_supported().
>
> Any better ideas for how to implement 3)?
And yeah, this is hard. So I'd just go for the low hanging fruit
for now and only implement 1) with a comment mentioning that
we are a little pessimistic.
next prev parent reply other threads:[~2019-01-15 17:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 13:22 [PATCH 0/3 v2] Fix virtio-blk issue with SWIOTLB Joerg Roedel
2019-01-15 13:22 ` [PATCH 1/3] swiotlb: Introduce swiotlb_max_mapping_size() Joerg Roedel
2019-01-15 13:22 ` [PATCH 2/3] dma: Introduce dma_max_mapping_size() Joerg Roedel
2019-01-15 13:37 ` Christoph Hellwig
2019-01-15 16:23 ` Joerg Roedel
2019-01-15 17:54 ` Christoph Hellwig [this message]
2019-01-15 13:22 ` [PATCH 3/3] virtio-blk: Consider dma_max_mapping_size() for maximum segment size Joerg Roedel
2019-01-16 14:05 ` Michael S. Tsirkin
2019-01-16 14:10 ` Joerg Roedel
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