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Index: head/sys/mips/mips/pmap.c
===================================================================
--- head/sys/mips/mips/pmap.c
+++ head/sys/mips/mips/pmap.c
@@ -3502,28 +3502,71 @@
PMAP_LOCK(pmap);
pte = pmap_pte(pmap, va);
- if (pte == NULL)
- panic("pmap_emulate_modified: can't find PTE");
-#ifdef SMP
- /* It is possible that some other CPU changed m-bit */
- if (!pte_test(pte, PTE_V) || pte_test(pte, PTE_D)) {
+
+ /*
+ * It is possible that some other CPU or thread changed the pmap while
+ * we weren't looking; in the SMP case, this is readily apparent, but
+ * it can even happen in the UP case, because we may have been blocked
+ * on PMAP_LOCK(pmap) above while someone changed this out from
+ * underneath us.
+ */
+
+ if (pte == NULL) {
+ /*
+ * This PTE's PTP (or one of its ancestors) has been reclaimed;
+ * trigger a full fault to reconstruct it via pmap_enter.
+ */
+ PMAP_UNLOCK(pmap);
+ return (1);
+ }
+
+ if (!pte_test(pte, PTE_V)) {
+ /*
+ * This PTE is no longer valid; the other thread or other
+ * processor must have arranged for our TLB to no longer
+ * have this entry, possibly by IPI, so no tlb_update is
+ * required. Fall out of the fast path and go take a
+ * general fault before retrying the instruction (or taking
+ * a signal).
+ */
+ PMAP_UNLOCK(pmap);
+ return (1);
+ }
+
+ if (pte_test(pte, PTE_D)) {
+ /*
+ * This PTE is valid and has the PTE_D bit asserted; since
+ * this is an increase in permission, we may have been expected
+ * to update the TLB lazily. Do so here and return, on the
+ * fast path, to retry the instruction.
+ */
tlb_update(pmap, va, *pte);
PMAP_UNLOCK(pmap);
return (0);
}
-#else
- if (!pte_test(pte, PTE_V) || pte_test(pte, PTE_D))
- panic("pmap_emulate_modified: invalid pte");
-#endif
+
if (pte_test(pte, PTE_RO)) {
+ /*
+ * This PTE is valid, not dirty, and read-only. Go take a
+ * full fault (most likely to upgrade this part of the address
+ * space to writeable).
+ */
PMAP_UNLOCK(pmap);
return (1);
}
- pte_set(pte, PTE_D);
- tlb_update(pmap, va, *pte);
+
if (!pte_test(pte, PTE_MANAGED))
panic("pmap_emulate_modified: unmanaged page");
+
+ /*
+ * PTE is valid, managed, not dirty, and not read-only. Set PTE_D
+ * and eagerly update the local TLB, returning on the fast path.
+ */
+
+ pte_set(pte, PTE_D);
+ tlb_update(pmap, va, *pte);
PMAP_UNLOCK(pmap);
+
return (0);
}

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