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 logic should be something like: if (hcd->localmem_pool || !hcd_uses_dma(hcd)) remap_pfn_range() else dma_mmap_coherent()