Re: macppc can't modify pages in swap

> Date: Sun, 23 Dec 2018 21:20:11 +0100 (CET)
> From: Mark Kettenis <[email protected]>
> 
> > Date: Sun, 23 Dec 2018 19:35:02 +0100 (CET)
> > From: Mark Kettenis <[email protected]>
> > 
> > > Date: Sun, 23 Dec 2018 12:26:17 +0100 (CET)
> > > From: Mark Kettenis <[email protected]>
> > > 
> > > 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.
> 
> I fear sombody else needs to test on an MP machine as my dual G4
> doesn't boot anymore :(.

And for those only on ppc@, here is the diff again.

Please test.


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);