On 5/14/20 2:46 AM, Greg KH wrote:
On Thu, May 14, 2020 at 08:31:58AM +0200, 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 logic should be something like:
if (hcd->localmem_pool || !hcd_uses_dma(hcd))
remap_pfn_range()
else
dma_mmap_coherent()
Ok, that's simple enough, patch is below.
Jeremy, any objection to this change?
No, thats fine but since I just translated usb_alloc_coherent() to
dma_map_coherent in my not fully away head. Putting this as
"usb_map_cohernet()" sort of makes more sense.
thanks,
greg k-h
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index b9db9812d6c5..d93d94d7ff50 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -251,9 +251,19 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
usbm->vma_use_count = 1;
INIT_LIST_HEAD(&usbm->memlist);
- if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle, size)) {
- dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
- return -EAGAIN;
+ if (hcd->localmem_pool || !hcd_uses_dma(hcd)) {
+ if (remap_pfn_range(vma, vma->vm_start,
+ virt_to_phys(usbm->mem) >> PAGE_SHIFT,
+ size, vma->vm_page_prot) < 0) {
+ dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
+ return -EAGAIN;
+ }
+ } else {
+ if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle,
+ size)) {
+ dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
+ return -EAGAIN;
+ }
}
vma->vm_flags |= VM_IO;
