> Date: Sun, 23 Dec 2018 12:26:17 +0100 (CET)
> From: Mark Kettenis <mark.kette...@xs4all.nl>
>
> That's a very good find. I think there still is a potential race in
> your diff on MP systems since you save the bits before removing the
> PTE from the has tables. I'll see if I can come up with a better diff.
So here is the diff I propose instead. This zaps the PTE before
unlinking. At that point the PTED_VA_MANAGED_M flag is still set so
the MOD/REF accounting will happen. A process running on the other
CPU can't put the PTE back into the hash as we still hold the lock on
the pmap.
Bootstrapping clang with this diff, and things are still running even
though I've hit swap. I'll give this a spin on an MP machine as well.
Index: arch/powerpc/powerpc/pmap.c
===================================================================
RCS file: /cvs/src/sys/arch/powerpc/powerpc/pmap.c,v
retrieving revision 1.168
diff -u -p -r1.168 pmap.c
--- arch/powerpc/powerpc/pmap.c 22 Oct 2018 17:31:25 -0000 1.168
+++ arch/powerpc/powerpc/pmap.c 23 Dec 2018 18:25:32 -0000
@@ -2067,7 +2067,9 @@ void
pmap_page_protect(struct vm_page *pg, vm_prot_t prot)
{
struct pte_desc *pted;
+ void *pte;
pmap_t pm;
+ int s;
if (prot == PROT_NONE) {
mtx_enter(&pg->mdpage.pv_mtx);
@@ -2097,6 +2099,11 @@ pmap_page_protect(struct vm_page *pg, vm
mtx_enter(&pg->mdpage.pv_mtx);
continue;
}
+
+ PMAP_HASH_LOCK(s);
+ if ((pte = pmap_ptedinhash(pted)) != NULL)
+ pte_zap(pte, pted);
+ PMAP_HASH_UNLOCK(s);
pted->pted_va &= ~PTED_VA_MANAGED_M;
LIST_REMOVE(pted, pted_pv_list);
