[Bug 215906] DMAR fault when connected usb hub (xhci_hcd)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=215906

--- Comment #22 from Michał Pecio (michal.pecio@gmail.com) ---
That's good to hear. Just to be sure, can you confirm that without this quirk
the problem still exists today, on the same machine running the same kernel?

This enables the XHCI_ZHAOXIN_TRB_FETCH quirk which allocates 8KB for each 4KB
transfer ring segment and leaves the upper 4KB empty, so that DMA accesses
beyond the 4KB segment end up hitting valid and harmless memory.

It wastes a few KB of memory per endpoint, and RasPI came up with a more
efficient solution, but this is something already implemented here so we could
try it immediately without patching.

BTW, there is speculation that the Zhaoxin bug may be caused by odd page size
requirements of some controllers. If your kernel has debugfs enabled, please
also post the output of:

grep PAGESIZE /sys/kernel/debug/usb/xhci/*/reg-op
lspci -nn |grep USB

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