Hi,
On 5/14/20 1:31 AM, Christoph Hellwig wrote:
On Thu, May 14, 2020 at 08:27:50AM +0200, Greg KH wrote:
On Thu, May 14, 2020 at 08:14:17AM +0200, Christoph Hellwig wrote:
Guys, can you please start formal thread on this? I have no
idea where this came from and what the rationale is. Btw, if the
pfn is crap in dma_direct_mmap then the dma_addr_t passed in is
crap, as it is derived from that. What is the caller, and how is
this triggered?
Ok, to summarize, commit 2bef9aed6f0e ("usb: usbfs: correct kernel->user
page attribute mismatch") changed a call from remap_pfn_range() to
dma_mmap_coherent() for usb data buffers being sent from userspace.
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().
The logic should be something like:
if (hcd->localmem_pool || !hcd_uses_dma(hcd))
remap_pfn_range()
else
dma_mmap_coherent()
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...
