[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC] virtio_ring: check dma_mem for xen_domain
On Wed, 23 Jan 2019, hch@xxxxxxxxxxxxx wrote: > On Wed, Jan 23, 2019 at 01:04:33PM -0800, Stefano Stabellini wrote: > > If vring_use_dma_api is actually supposed to return true when > > dma_dev->dma_mem is set, then both Peng's patch and the patch I wrote > > are not fixing the real issue here. > > > > I don't know enough about remoteproc to know where the problem actually > > lies though. > > The problem is the following: > > Devices can declare a specific memory region that they want to use when > the driver calls dma_alloc_coherent for the device, this is done using > the shared-dma-pool DT attribute, which comes in two variants that > would be a little to much to explain here. > > remoteproc makes use of that because apparently the device can > only communicate using that region. But it then feeds back memory > obtained with dma_alloc_coherent into the virtio code. For that > it calls vmalloc_to_page on the dma_alloc_coherent, which is a huge > no-go for the ĐMA API and only worked accidentally on a few platform, > and apparently arm64 just changed a few internals that made it stop > working for remoteproc. > > The right answer is to not use the DMA API to allocate memory from > a device-speficic region, but to tie the driver directly into the > DT reserved memory API in a way that allows it to easilt obtain > a struct device for it. If I understand correctly, Peng should be able to reproduce the problem on native Linux without any Xen involvement simply by forcing vring_use_dma_api to return true. Peng, can you confirm? And the right fix is not to call vmalloc_to_page on a dma_alloc_coherent buffer -- I don't know about the recent changes on arm64, but that's not going to work with arm32 either AFAIK. Given that I don't have a repro, I'll leave it to Peng and/or others to send the appropriate patch for remoteproc. > This is orthogonal to another issue, and that is that hardware > virtio devices really always need to use the DMA API, otherwise > we'll bypass such features as the device specific DMA pools, > DMA offsets, cache flushing, etc, etc. I understand, I'll drop my patch. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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