On 2022-05-17 9:06 a.m., Rolf Eike Beer wrote:
@@ -450,10 +452,12 @@ handle_nadtlb_fault(struct pt_regs *regs) fallthrough; case 0x380: /* PDC and FIC instructions */ +#ifdef DEBUG_NATLB if (printk_ratelimit()) { - pr_warn("BUG: nullifying cache flush/purgeinstruction\n");+ pr_warn("WARNING: nullifying cache flush/purge instruction\n");show_regs(regs); } +#endif if (insn & 0x20) { /* Base modification */ breg = (insn >> 21) & 0x1f;This surely deserves it's own commit as it has nothing to do with the actual change. I wonder if it is actually intended to go upstream or if this was just a local debug hack?
I changed "BUG" to "WARNING" and disabled the message because it triggers occasionally in spite of the check in flush_cache_page_if_present. The pte value extracted for the "from" page in copy_user_highpage is racy and occasionally the pte is cleared before the flush is complete. I assume that the page is simultaneously flushed by flush_cache_mm before the pte is cleared as nullifying the fdc doesn't seem to cause problems. I investigated various locking scenarios but I wasn't able to find a way to sequence the flushes. This code is called for every COW break and locks impact performance. This is related to this patch because we need the pte on PA8800/PA8900 to flush using the vma context. I have also seen this from copy_to_user_page and copy_from_user_page. The messages appear infrequently when enabled. Dave -- John David Anglin dave.anglin@xxxxxxxx
