Do only one VP lookup when removing a page.

This simplify pmap_remove() & friends by re-using an already fetched PTE
descriptor.

There's currently a race on MP system where one CPU can reuse a pted
while another one is still trying to insert it in the HASH.  This commit
starts reducing the number of pmap_vp_lookup() calls to help fix this
race.

ok kettenis@, deraadt@, dlg@

diff --git a/sys/arch/powerpc/powerpc/pmap.c b/sys/arch/powerpc/powerpc/pmap.c
index 92cd81c..ccef94a 100644 (file)
--- a/sys/arch/powerpc/powerpc/pmap.c
+++ b/sys/arch/powerpc/powerpc/pmap.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: pmap.c,v 1.147 2015/06/05 09:09:58 mpi Exp $ */
+/*     $OpenBSD: pmap.c,v 1.148 2015/06/05 09:18:50 mpi Exp $ */
 
 /*
  * Copyright (c) 2001, 2002, 2007 Dale Rahn.
@@ -164,7 +164,7 @@ void pmap_syncicache_user_virt(pmap_t pm, vaddr_t va);
 
 void _pmap_kenter_pa(vaddr_t va, paddr_t pa, vm_prot_t prot, int flags,
     int cache);
-void pmap_remove_pg(pmap_t pm, vaddr_t va);
+void pmap_remove_pted(pmap_t, struct pte_desc *);
 
 /* setup/initialization functions */
 void pmap_avail_setup(void);
@@ -547,7 +547,7 @@ pmap_enter(pmap_t pm, vaddr_t va, paddr_t pa, vm_prot_t prot, int flags)
 
        pted = pmap_vp_lookup(pm, va);
        if (pted && PTED_VALID(pted)) {
-               pmap_remove_pg(pm, va);
+               pmap_remove_pted(pm, pted);
                /* we lost our pted if it was user */
                if (pm != pmap_kernel())
                        pted = pmap_vp_lookup(pm, va);
@@ -643,6 +643,7 @@ pmap_remove(pmap_t pm, vaddr_t va, vaddr_t endva)
        int i_vp2, s_vp2, e_vp2;
        struct pmapvp *vp1;
        struct pmapvp *vp2;
+       struct pte_desc *pted;
 
        /* I suspect that if this loop were unrolled better 
         * it would have better performance, testing i_sr and i_vp1
@@ -679,15 +680,12 @@ pmap_remove(pmap_t pm, vaddr_t va, vaddr_t endva)
                        if ((i_sr == e_sr) && (i_vp1 == e_vp1))
                                e_vp2 = VP_IDX2(endva);
                        else
-                               e_vp2 = VP_IDX2_SIZE; 
+                               e_vp2 = VP_IDX2_SIZE;
 
                        for (i_vp2 = s_vp2; i_vp2 < e_vp2; i_vp2++) {
-                               if (vp2->vp[i_vp2] != NULL) {
-                                       pmap_remove_pg(pm,
-                                           (i_sr << VP_SR_POS) |
-                                           (i_vp1 << VP_IDX1_POS) |
-                                           (i_vp2 << VP_IDX2_POS));
-                               }
+                               pted = vp2->vp[i_vp2];
+                               if (pted && PTED_VALID(pted))
+                                       pmap_remove_pted(pm, pted);
                        }
                }
        }
@@ -696,27 +694,16 @@ pmap_remove(pmap_t pm, vaddr_t va, vaddr_t endva)
  * remove a single mapping, notice that this code is O(1)
  */
 void
-pmap_remove_pg(pmap_t pm, vaddr_t va)
+pmap_remove_pted(pmap_t pm, struct pte_desc *pted)
 {
-       struct pte_desc *pted;
+       KASSERT(pm == pted->pted_pmap);
 
-       if (pm == pmap_kernel()) {
-               pted = pmap_vp_lookup(pm, va);
-               if (pted == NULL || !PTED_VALID(pted)) {
-                       return;
-               }
-       } else {
-               pted = pmap_vp_remove(pm, va);
-               if (pted == NULL || !PTED_VALID(pted)) {
-                       return;
-               }
-       }
        pm->pm_stats.resident_count--;
 
        pmap_hash_remove(pted);
 
        if (pted->pted_va & PTED_VA_EXEC_M) {
-               u_int sn = VP_SR(va);
+               u_int sn = VP_SR(pted->pted_va);
 
                pted->pted_va &= ~PTED_VA_EXEC_M;
                pm->pm_exec[sn]--;
@@ -732,8 +719,10 @@ pmap_remove_pg(pmap_t pm, vaddr_t va)
        if (PTED_MANAGED(pted))
                pmap_remove_pv(pted);
 
-       if (pm != pmap_kernel())
+       if (pm != pmap_kernel()) {
+               (void)pmap_vp_remove(pm, pted->pted_va);
                pool_put(&pmap_pted_pool, pted);
+       }
 }
 
 /*
@@ -762,7 +751,7 @@ pmap_kenter_pa(vaddr_t va, paddr_t pa, vm_prot_t prot)
 
        pted = pmap_vp_lookup(pm, va);
        if (pted && PTED_VALID(pted))
-               pmap_remove_pg(pm, va); /* pted is reused */
+               pmap_remove_pted(pm, pted); /* pted is reused */
 
        pm->pm_stats.resident_count++;
 
@@ -819,8 +808,13 @@ pmap_kenter_pa(vaddr_t va, paddr_t pa, vm_prot_t prot)
 void
 pmap_kremove(vaddr_t va, vsize_t len)
 {
-       for (len >>= PAGE_SHIFT; len >0; len--, va += PAGE_SIZE)
-               pmap_remove_pg(pmap_kernel(), va);
+       struct pte_desc *pted;
+
+       for (len >>= PAGE_SHIFT; len > 0; len--, va += PAGE_SIZE) {
+               pted = pmap_vp_lookup(pmap_kernel(), va);
+               if (pted && PTED_VALID(pted))
+                       pmap_remove_pted(pmap_kernel(), pted);
+       }
 }
 
 void
@@ -2124,7 +2118,7 @@ pmap_page_protect(struct vm_page *pg, vm_prot_t prot)
        if (prot == PROT_NONE) {
                while (!LIST_EMPTY(&(pg->mdpage.pv_list))) {
                        pted = LIST_FIRST(&(pg->mdpage.pv_list));
-                       pmap_remove_pg(pted->pted_pmap, pted->pted_va);
+                       pmap_remove_pted(pted->pted_pmap, pted);
                }
                /* page is being reclaimed, sync icache next use */
                atomic_clearbits_int(&pg->pg_flags, PG_PMAP_EXE);