This patch fixes crashes when usbmon attempts to access GART aperture.
The old code attempted to take a bus address and convert it into a
virtual address, which clearly was impossible on systems with actual
IOMMUs. Let us not persist in this foolishness, and use transfer_buffer
in all cases instead.
I think downsides are negligible. The ones I see are:
- A driver may pass an address of one buffer down as transfer_buffer,
and entirely different entity mapped for DMA, resulting in misleading
output of usbmon. Note, however, that PIO based controllers would
do transfer the same data that usbmon sees here.
- Out of tree drivers may crash usbmon if they store garbage in
transfer_buffer. I inspected the in-tree drivers, and clarified
the documentation in comments.
- Drivers that use get_user_pages will not be possible to monitor.
I only found one driver with this problem (drivers/staging/rspiusb).
- Same happens with with usb_storage transferring from highmem, but
it works fine on 64-bit systems, so I think it's not a concern.
At least we don't crash anymore.
Why didn't we do this in 2.6.10? That's because back in those days
it was popular not to fill in transfer_buffer, so almost all
traffic would be invisible (e.g. all of HID was like that).
But now, the tree is almost 100% PIO friendly, so we can do the
right thing at last.
Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
4e9e920035