On Thu, May 14, 2020 at 06:10:03AM -0500, Jeremy Linton wrote: >> I only need to look at the commit for 3 seconds to tell you that it is >> completely buggy. While using dma_mmap_coherent is fundamentally the >> right thing and absolutely required for dma_alloc_* allocations, USB >> also uses it's own local gen pool allocator or plain kmalloc for not >> DMA capable controller. This need to use remap_pfn_range. I'm pretty >> sure you hit one of those cases. > > ? The code path in question is usbdev_mmap() and the allocation is done ~13 > lines lines before as a usb_alloc_coherent(). And did you take a look at how usb_alloc_coherent is implemented? That should make it completely obvious that not all allocations come from dma_alloc_*. > That sort of makes sense, except for the above, and the fact that I would > imagine the dma_mmap_coherent should be dealing with that case. I'm not > really clear about the details of the GCE usb device here, but my first > guess at this was the dma_pgprot() in dma_direct_mmap() is incorrectly > picking a pgprot... No, dma_mmap_* / dma_direct_mmap has absolutely no business dealing with memory that did not come from the DMA allocator.
