On 29 May 2019, at 22:00, James Clarke <jrtc27@xxxxxxxxxx> wrote: > On 29 May 2019, at 21:23, David Miller <davem@xxxxxxxxxxxxx> wrote: >> >> From: Meelis Roos <mroos@xxxxxxxx> >> Date: Wed, 29 May 2019 22:08:26 +0300 >> >>> Bisecting led me to 4.9 merge window and this patch that broke it: >>> >>> a74ad5e660a9ee1d071665e7e8ad822784a2dc7f is the first bad commit >>> commit a74ad5e660a9ee1d071665e7e8ad822784a2dc7f >>> Author: David S. Miller <davem@xxxxxxxxxxxxx> >>> Date: Thu Oct 27 09:04:54 2016 -0700 >>> >>> sparc64: Handle extremely large kernel TLB range flushes more >>> gracefully. >> >> Thank you, I will take a close look at this ASAP. > > Perhaps I'm being stupid, but the first hunk in xcall_flush_tlb_kernel_range > looks wrong to me. %g2 previously contained PAGE_SIZE-1, but is now clobbered > by the new srlx, setting %g2 to (aligned_end-aligned_start)>>18. If the > brnz %g2 is taken, %g2 gets overwritten, so it's not a problem, but if the > branch *isn't* taken, then %g2 is zero, so the add %g2, 1, %g2 in the delay > slot of the branch sets %g2 to 1. However, prior to this commit, %g2 would then > have had the value PAGE_SIZE, and the following code to do a page-by-page flush > assumes this, using it as the amount to step through. Rather than stepping > through page-by-page (with offset 0x20 to indicate nucleus), we will step > through the loop byte-by-byte, so some iterations will have low bit > combinations for things other than a nucleus page demap operation. This same > bug is replicated in the new __cheetah_xcall_flush_tlb_kernel_range. Meelis, could you please try the attached patch to see if it fixes the issue? David, I don't actually see why we need this alignment code in the first place. The only call to the xcall is in smp_flush_tlb_kernel_range which already rounds the start and end to multiples of the page size, so I believe we should be able to delete the first four instructions of the 3 different implementations? The non-xcall variants already skip doing this. Regards, James
Attachment:
0001-sparc64-Fix-regression-in-non-hypervisor-TLB-flush-x.patch
Description: Binary data
