MIPS: Fix MSA ld unaligned failure cases
Copying the content of an MSA vector from user memory may involve TLB faults & mapping in pages. This will fail when preemption is disabled due to an inability to acquire mmap_sem from do_page_fault, which meant such vector loads to unmapped pages would always fail to be emulated. Fix this by disabling preemption later only around the updating of vector register state. This change does however introduce a race between performing the load into thread context & the thread being preempted, saving its current live context & clobbering the loaded value. This should be a rare occureence, so optimise for the fast path by simply repeating the load if we are preempted. Additionally if the copy failed then the failure path was taken with preemption left disabled, leading to the kernel typically encountering further issues around sleeping whilst atomic. The change to where preemption is disabled avoids this issue. Fixes: e4aa1f15 "MIPS: MSA unaligned memory access support" Reported-by:James Hogan <james.hogan@imgtec.com> Signed-off-by:
Paul Burton <paul.burton@imgtec.com> Reviewed-by:
James Hogan <james.hogan@imgtec.com> Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> Cc: Maciej W. Rozycki <macro@linux-mips.org> Cc: James Cowgill <James.Cowgill@imgtec.com> Cc: Markos Chandras <markos.chandras@imgtec.com> Cc: stable <stable@vger.kernel.org> # v4.3 Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/12345/ Signed-off-by:
Ralf Baechle <ralf@linux-mips.org>
parent
19fb5818
Please register or sign in to comment