From: Robin Murphy <robin.murphy@arm.com>
To: Jason Gunthorpe <jgg@nvidia.com>, Christoph Hellwig <hch@infradead.org>
Cc: "Leon Romanovsky" <leon@kernel.org>,
kvm@vger.kernel.org, linux-rdma@vger.kernel.org,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Oded Gabbay" <ogabbay@kernel.org>,
"Cornelia Huck" <cohuck@redhat.com>,
dri-devel@lists.freedesktop.org,
"Christian König" <christian.koenig@amd.com>,
linaro-mm-sig@lists.linaro.org,
"Alex Williamson" <alex.williamson@redhat.com>,
"Maor Gottlieb" <maorg@nvidia.com>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
linux-media@vger.kernel.org
Subject: Re: [PATCH v2 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf
Date: Wed, 7 Sep 2022 16:01:54 +0100 [thread overview]
Message-ID: <de00b89e-c676-1e71-c21b-dd3d13917b48@arm.com> (raw)
In-Reply-To: <YxiPh4u/92chN02C@nvidia.com>
On 2022-09-07 13:33, Jason Gunthorpe wrote:
> On Wed, Sep 07, 2022 at 05:05:57AM -0700, Christoph Hellwig wrote:
>> On Tue, Sep 06, 2022 at 08:48:28AM -0300, Jason Gunthorpe wrote:
>>> Right, this whole thing is the "standard" that dmabuf has adopted
>>> instead of the struct pages. Once the AMD GPU driver started doing
>>> this some time ago other drivers followed.
>>
>> But it is simple wrong. The scatterlist requires struct page backing.
>> In theory a physical address would be enough, but when Dan Williams
>> sent patches for that Linus shot them down.
>
> Yes, you said that, and I said that when the AMD driver first merged
> it - but it went in anyhow and now people are using it in a bunch of
> places.
>
> I'm happy that Christian wants to start trying to fix it, and will
> help him, but it doesn't really impact this. Whatever fix is cooked up
> will apply equally to vfio and habana.
We've just added support for P2P segments in scatterlists, can that not
be used here?
Robin.
>> That being said the scatterlist is the wrong interface here (and
>> probably for most of it's uses). We really want a lot-level struct
>> with just the dma_address and length for the DMA side, and leave it
>> separate from that what is used to generate it (in most cases that
>> would be a bio_vec).
>
> Oh definitely
>
>>> Now we have struct pages, almost, but I'm not sure if their limits are
>>> compatible with VFIO? This has to work for small bars as well.
>>
>> Why would small BARs be problematic for the pages? The pages are more
>> a problem for gigantic BARs do the memory overhead.
>
> How do I get a struct page * for a 4k BAR in vfio?
>
> The docs say:
>
> ..hotplug api on memory block boundaries. The implementation relies on
> this lack of user-api constraint to allow sub-section sized memory
> ranges to be specified to :c:func:`arch_add_memory`, the top-half of
> memory hotplug. Sub-section support allows for 2MB as the cross-arch
> common alignment granularity for :c:func:`devm_memremap_pages`.
>
> Jason
next prev parent reply other threads:[~2022-09-07 15:02 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-31 23:12 [PATCH v2 0/4] Allow MMIO regions to be exported through dma-buf Jason Gunthorpe
2022-08-31 23:12 ` [PATCH v2 1/4] dma-buf: Add dma_buf_try_get() Jason Gunthorpe
2022-09-01 7:55 ` Christian König
2022-09-06 16:44 ` Jason Gunthorpe
2022-09-06 17:52 ` Christian König
2022-08-31 23:12 ` [PATCH v2 2/4] vfio: Add vfio_device_get() Jason Gunthorpe
2022-08-31 23:12 ` [PATCH v2 3/4] vfio_pci: Do not open code pci_try_reset_function() Jason Gunthorpe
2022-08-31 23:12 ` [PATCH v2 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf Jason Gunthorpe
[not found] ` <YxcYGzPv022G2vLm@infradead.org>
2022-09-06 10:38 ` Christian König
2022-09-06 11:48 ` Jason Gunthorpe
2022-09-06 12:34 ` Oded Gabbay
2022-09-06 17:59 ` Jason Gunthorpe
2022-09-06 19:44 ` Oded Gabbay
[not found] ` <YxiJJYtWgh1l0wxg@infradead.org>
2022-09-07 12:33 ` Jason Gunthorpe
[not found] ` <Yxiq5sjf/qA7xS8A@infradead.org>
2022-09-07 14:46 ` Oded Gabbay
2022-09-07 15:23 ` Jason Gunthorpe
[not found] ` <Yxi5h09JAzIo4Kh8@infradead.org>
2022-09-07 16:12 ` Jason Gunthorpe
[not found] ` <Yxs+k6psNfBLDqdv@infradead.org>
2022-09-09 14:09 ` Jason Gunthorpe
2022-09-07 16:31 ` Robin Murphy
2022-09-07 16:47 ` Jason Gunthorpe
2022-09-07 17:03 ` Dan Williams
2022-09-07 15:01 ` Robin Murphy [this message]
[not found] ` <YxiIkh/yeWQkZ54x@infradead.org>
2022-09-07 15:08 ` Christian König
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