1. Disable the lazy allocation of lev1map in pmap_enter(), instead doing
it in pmap_create(), and freeing the lev1map in pmap_destroy(). This means that pm_lev1map is consistent for the life of the pmap. 2. pmap_extract() now uses vtophys() for the kernel pmap. This avoids having to lock the kernel pmap, since kernel PT pages are never freed. 3. Because of (1), pmap_asn_alloc() no longer needs to operate on a locked pmap; pm_lev1map will never change over the life of the pmap, and all other access to the pmap is done in per-CPU fields or with atomic operations. 4. Because of (3), pmap_activate() no longer needs to lock the pmap to do its work, thus eliminating the deadlock with sched_lock described in PR port-alpha/25599. This is safe because we are guaranteed that the pmap is still alive, since by definition an LWP that uses that it is about to run. Thanks to Michael Hitch for the analysis, and Michael and Ragge for testing.
This commit is contained in:
thorpej
parent
3692d77541
commit
bdfafa03cd
@ -1,4 +1,4 @@
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/* $NetBSD: pmap.c,v 1.210 2005/06/01 16:09:45 drochner Exp $ */
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/* $NetBSD: pmap.c,v 1.211 2005/07/26 04:11:53 thorpej Exp $ */
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/*-
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* Copyright (c) 1998, 1999, 2000, 2001 The NetBSD Foundation, Inc.
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@ -145,7 +145,7 @@
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#include <sys/cdefs.h> /* RCS ID & Copyright macro defns */
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__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.210 2005/06/01 16:09:45 drochner Exp $");
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__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.211 2005/07/26 04:11:53 thorpej Exp $");
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#include <sys/param.h>
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#include <sys/systm.h>
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@ -524,6 +524,17 @@ void pmap_physpage_free(paddr_t);
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int pmap_physpage_addref(void *);
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int pmap_physpage_delref(void *);
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/*
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* Define PMAP_NO_LAZY_LEV1MAP in order to have a lev1map allocated
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* in pmap_create(), rather than when the first mapping is entered.
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* This causes pmaps to use an extra page of memory if no mappings
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* are entered in them, but in practice this is probably not going
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* to be a problem, and it allows us to avoid locking pmaps in
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* pmap_activate(), which in turn allows us to avoid a deadlock with
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* sched_lock via cpu_switch().
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*/
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#define PMAP_NO_LAZY_LEV1MAP
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/*
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* PMAP_ISACTIVE{,_TEST}:
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*
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@ -1207,6 +1218,11 @@ pmap_create(void)
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TAILQ_INSERT_TAIL(&pmap_all_pmaps, pmap, pm_list);
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simple_unlock(&pmap_all_pmaps_slock);
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#ifdef PMAP_NO_LAZY_LEV1MAP
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i = pmap_lev1map_create(pmap, cpu_number());
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KASSERT(i == 0);
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#endif
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return (pmap);
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}
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@ -1240,14 +1256,16 @@ pmap_destroy(pmap_t pmap)
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TAILQ_REMOVE(&pmap_all_pmaps, pmap, pm_list);
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simple_unlock(&pmap_all_pmaps_slock);
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#ifdef DIAGNOSTIC
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#ifdef PMAP_NO_LAZY_LEV1MAP
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pmap_lev1map_destroy(pmap, cpu_number());
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#endif
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/*
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* Since the pmap is supposed to contain no valid
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* mappings at this point, this should never happen.
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* mappings at this point, we should always see
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* kernel_lev1map here.
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*/
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if (pmap->pm_lev1map != kernel_lev1map)
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panic("pmap_destroy: pmap still contains valid mappings");
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#endif
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KASSERT(pmap->pm_lev1map == kernel_lev1map);
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pool_put(&pmap_pmap_pool, pmap);
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}
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@ -1685,6 +1703,9 @@ pmap_enter(pmap_t pmap, vaddr_t va, paddr_t pa, vm_prot_t prot, int flags)
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panic("pmap_enter: user pmap, invalid va 0x%lx", va);
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#endif
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#ifdef PMAP_NO_LAZY_LEV1MAP
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KASSERT(pmap->pm_lev1map != kernel_lev1map);
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#else
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/*
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* If we're still referencing the kernel kernel_lev1map,
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* create a new level 1 page table. A reference will be
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@ -1715,6 +1736,7 @@ pmap_enter(pmap_t pmap, vaddr_t va, paddr_t pa, vm_prot_t prot, int flags)
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panic("pmap_enter: unable to create lev1map");
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}
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}
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#endif /* PMAP_NO_LAZY_LEV1MAP */
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/*
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* Check to see if the level 1 PTE is valid, and
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@ -2128,6 +2150,22 @@ pmap_extract(pmap_t pmap, vaddr_t va, paddr_t *pap)
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if (pmapdebug & PDB_FOLLOW)
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printf("pmap_extract(%p, %lx) -> ", pmap, va);
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#endif
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/*
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* Take a faster path for the kernel pmap. Avoids locking,
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* handles K0SEG.
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*/
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if (pmap == pmap_kernel()) {
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pa = vtophys(va);
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if (pap != NULL)
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*pap = pa;
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#ifdef DEBUG
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if (pmapdebug & PDB_FOLLOW)
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printf("0x%lx (kernel vtophys)\n", pa);
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#endif
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return (pa != 0); /* XXX */
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}
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PMAP_LOCK(pmap);
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l1pte = pmap_l1pte(pmap, va);
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@ -2238,21 +2276,21 @@ pmap_activate(struct lwp *l)
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printf("pmap_activate(%p)\n", l);
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#endif
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#ifndef PMAP_NO_LAZY_LEV1MAP
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PMAP_LOCK(pmap);
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#endif
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/*
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* Mark the pmap in use by this processor.
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*/
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/* Mark the pmap in use by this processor. */
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atomic_setbits_ulong(&pmap->pm_cpus, (1UL << cpu_id));
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/*
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* Allocate an ASN.
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*/
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/* Allocate an ASN. */
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pmap_asn_alloc(pmap, cpu_id);
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PMAP_ACTIVATE(pmap, l, cpu_id);
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#ifndef PMAP_NO_LAZY_LEV1MAP
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PMAP_UNLOCK(pmap);
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#endif
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}
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/*
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@ -3254,12 +3292,18 @@ pmap_lev1map_create(pmap_t pmap, long cpu_id)
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panic("pmap_lev1map_create: pmap uses non-reserved ASN");
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#endif
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#ifdef PMAP_NO_LAZY_LEV1MAP
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/* Being called from pmap_create() in this case; we can sleep. */
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l1pt = pool_cache_get(&pmap_l1pt_cache, PR_WAITOK);
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#else
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l1pt = pool_cache_get(&pmap_l1pt_cache, PR_NOWAIT);
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#endif
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if (l1pt == NULL)
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return (ENOMEM);
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pmap->pm_lev1map = l1pt;
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#ifndef PMAP_NO_LAZY_LEV1MAP /* guaranteed not to be active */
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/*
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* The page table base has changed; if the pmap was active,
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* reactivate it.
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@ -3269,6 +3313,7 @@ pmap_lev1map_create(pmap_t pmap, long cpu_id)
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PMAP_ACTIVATE(pmap, curlwp, cpu_id);
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}
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PMAP_LEV1MAP_SHOOTDOWN(pmap, cpu_id);
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#endif /* ! PMAP_NO_LAZY_LEV1MAP */
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return (0);
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}
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@ -3294,6 +3339,7 @@ pmap_lev1map_destroy(pmap_t pmap, long cpu_id)
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*/
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pmap->pm_lev1map = kernel_lev1map;
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#ifndef PMAP_NO_LAZY_LEV1MAP /* pmap is being destroyed */
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/*
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* The page table base has changed; if the pmap was active,
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* reactivate it. Note that allocation of a new ASN is
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@ -3316,6 +3362,7 @@ pmap_lev1map_destroy(pmap_t pmap, long cpu_id)
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if (PMAP_ISACTIVE(pmap, cpu_id))
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PMAP_ACTIVATE(pmap, curlwp, cpu_id);
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PMAP_LEV1MAP_SHOOTDOWN(pmap, cpu_id);
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#endif /* ! PMAP_NO_LAZY_LEV1MAP */
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/*
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* Free the old level 1 page table page.
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@ -3554,11 +3601,13 @@ pmap_l1pt_delref(pmap_t pmap, pt_entry_t *l1pte, long cpu_id)
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#endif
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if (pmap_physpage_delref(l1pte) == 0) {
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#ifndef PMAP_NO_LAZY_LEV1MAP
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/*
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* No more level 2 tables left, go back to the global
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* kernel_lev1map.
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*/
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pmap_lev1map_destroy(pmap, cpu_id);
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#endif /* ! PMAP_NO_LAZY_LEV1MAP */
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}
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}
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@ -3590,6 +3639,13 @@ pmap_asn_alloc(pmap_t pmap, long cpu_id)
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* kernel mappings exist in that map, and all kernel mappings
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* have PG_ASM set. If the pmap eventually gets its own
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* lev1map, an ASN will be allocated at that time.
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*
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* #ifdef PMAP_NO_LAZY_LEV1MAP
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* Only the kernel pmap will reference kernel_lev1map. Do the
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* same old fixups, but note that we no longer need the pmap
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* to be locked if we're in this mode, since pm_lev1map will
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* never change.
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* #endif
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*/
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if (pmap->pm_lev1map == kernel_lev1map) {
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#ifdef DEBUG
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@ -3610,11 +3666,7 @@ pmap_asn_alloc(pmap_t pmap, long cpu_id)
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*/
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pma->pma_asn = PMAP_ASN_RESERVED;
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#else
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#ifdef DIAGNOSTIC
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if (pma->pma_asn != PMAP_ASN_RESERVED)
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panic("pmap_asn_alloc: kernel_lev1map without "
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"PMAP_ASN_RESERVED");
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#endif
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KASSERT(pma->pma_asn == PMAP_ASN_RESERVED);
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#endif /* MULTIPROCESSOR */
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return;
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}
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