On 5/14/20 6:14 AM, Christoph Hellwig wrote:
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_*.
No, your right, I noticed/remembered the usb_alloc vs dma_alloc
difference right after sending that email, and was just about to say so.
Sorry, you right.
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.
