svn commit: r360810 - stable/12/sys/mips/mips
Mark Johnston
markj at FreeBSD.org
Fri May 8 14:10:51 UTC 2020
Author: markj
Date: Fri May 8 14:10:47 2020
New Revision: 360810
URL: https://svnweb.freebsd.org/changeset/base/360810
Log:
MFC r360280:
Fix a race between _pmap_unwire_ptp() and MipsDoTLBMiss().
Modified:
stable/12/sys/mips/mips/pmap.c
Directory Properties:
stable/12/ (props changed)
Modified: stable/12/sys/mips/mips/pmap.c
==============================================================================
--- stable/12/sys/mips/mips/pmap.c Fri May 8 14:10:29 2020 (r360809)
+++ stable/12/sys/mips/mips/pmap.c Fri May 8 14:10:47 2020 (r360810)
@@ -975,18 +975,26 @@ static void
_pmap_unwire_ptp(pmap_t pmap, vm_offset_t va, vm_page_t m)
{
pd_entry_t *pde;
+ vm_offset_t sva, eva;
PMAP_LOCK_ASSERT(pmap, MA_OWNED);
/*
* unmap the page table page
*/
#ifdef __mips_n64
- if (m->pindex < NUPDE)
+ if (m->pindex < NUPDE) {
pde = pmap_pde(pmap, va);
- else
+ sva = va & ~PDRMASK;
+ eva = sva + NBPDR;
+ } else {
pde = pmap_segmap(pmap, va);
+ sva = va & ~SEGMASK;
+ eva = sva + NBSEG;
+ }
#else
pde = pmap_pde(pmap, va);
+ sva = va & ~SEGMASK;
+ eva = sva + NBSEG;
#endif
*pde = 0;
pmap->pm_stats.resident_count--;
@@ -997,12 +1005,22 @@ _pmap_unwire_ptp(pmap_t pmap, vm_offset_t va, vm_page_
vm_page_t pdpg;
/*
- * Recursively decrement next level pagetable refcount
+ * Recursively decrement next level pagetable refcount.
+ * Either that shoots down a larger range from TLBs (below)
+ * or we're to shoot down just the page in question.
*/
pdp = (pd_entry_t *)*pmap_segmap(pmap, va);
pdpg = PHYS_TO_VM_PAGE(MIPS_DIRECT_TO_PHYS(pdp));
- pmap_unwire_ptp(pmap, va, pdpg);
+ if (!pmap_unwire_ptp(pmap, va, pdpg)) {
+ pmap_invalidate_range(pmap, sva, eva);
+ }
+ } else {
+ /* Segmap entry shootdown */
+ pmap_invalidate_range(pmap, sva, eva);
}
+#else
+ /* Segmap entry shootdown */
+ pmap_invalidate_range(pmap, sva, eva);
#endif
/*
@@ -1455,7 +1473,15 @@ pmap_pv_reclaim(pmap_t locked_pmap)
if (TAILQ_EMPTY(&m->md.pv_list))
vm_page_aflag_clear(m, PGA_WRITEABLE);
pc->pc_map[field] |= 1UL << bit;
- pmap_unuse_pt(pmap, va, *pde);
+
+ /*
+ * For simplicity, we will unconditionally shoot
+ * down TLBs either at the end of this function
+ * or at the top of the loop above if we switch
+ * to a different pmap.
+ */
+ (void)pmap_unuse_pt(pmap, va, *pde);
+
freed++;
}
}
@@ -1684,6 +1710,23 @@ pmap_try_insert_pv_entry(pmap_t pmap, vm_page_t mpte,
/*
* pmap_remove_pte: do the things to unmap a page in a process
+ *
+ * Returns true if this was the last PTE in the PT (and possibly the last PT in
+ * the PD, and possibly the last PD in the segmap), in which case...
+ *
+ * 1) the TLB has been invalidated for the whole PT's span (at least),
+ * already, to ensure that MipsDoTLBMiss does not attempt to follow a
+ * dangling pointer into a freed page. No additional TLB shootdown is
+ * required.
+ *
+ * 2) if this removal was part of a sweep to remove PTEs, it is safe to jump
+ * to the PT span boundary and continue.
+ *
+ * 3) The given pde may now point onto a freed page and must not be
+ * dereferenced
+ *
+ * If the return value is false, the TLB has not been shot down (and the segmap
+ * entry, PD, and PT all remain in place).
*/
static int
pmap_remove_pte(struct pmap *pmap, pt_entry_t *ptq, vm_offset_t va,
@@ -1752,8 +1795,12 @@ pmap_remove_page(struct pmap *pmap, vm_offset_t va)
if (!pte_test(ptq, PTE_V))
return;
- (void)pmap_remove_pte(pmap, ptq, va, *pde);
- pmap_invalidate_page(pmap, va);
+ /*
+ * Remove this PTE from the PT. If this is the last one, then
+ * the TLB has already been shot down, so don't bother again
+ */
+ if (!pmap_remove_pte(pmap, ptq, va, *pde))
+ pmap_invalidate_page(pmap, va);
}
/*
@@ -1767,7 +1814,9 @@ pmap_remove(pmap_t pmap, vm_offset_t sva, vm_offset_t
{
pd_entry_t *pde, *pdpe;
pt_entry_t *pte;
- vm_offset_t va, va_next;
+ vm_offset_t va_next;
+ vm_offset_t va_init, va_fini;
+ bool need_tlb_shootdown;
/*
* Perform an unsynchronized read. This is, however, safe.
@@ -1796,6 +1845,8 @@ pmap_remove(pmap_t pmap, vm_offset_t sva, vm_offset_t
continue;
}
#endif
+
+ /* Scan up to the end of the page table pointed to by pde */
va_next = (sva + NBPDR) & ~PDRMASK;
if (va_next < sva)
va_next = eva;
@@ -1812,25 +1863,44 @@ pmap_remove(pmap_t pmap, vm_offset_t sva, vm_offset_t
if (va_next > eva)
va_next = eva;
- va = va_next;
+ need_tlb_shootdown = false;
+ va_init = sva;
+ va_fini = va_next;
for (pte = pmap_pde_to_pte(pde, sva); sva != va_next; pte++,
sva += PAGE_SIZE) {
+
+ /* Skip over invalid entries; no need to shootdown */
if (!pte_test(pte, PTE_V)) {
- if (va != va_next) {
- pmap_invalidate_range(pmap, va, sva);
- va = va_next;
- }
+ /*
+ * If we have not yet found a valid entry, then
+ * we can move the lower edge of the region to
+ * invalidate to the next PTE.
+ */
+ if (!need_tlb_shootdown)
+ va_init = sva + PAGE_SIZE;
continue;
}
- if (va == va_next)
- va = sva;
+
+ /*
+ * A valid entry; the range we are shooting down must
+ * include this page. va_fini is used instead of sva
+ * so that if the range ends with a run of !PTE_V PTEs,
+ * but doesn't clear out so much that pmap_remove_pte
+ * removes the entire PT, we won't include these !PTE_V
+ * entries in the region to be shot down.
+ */
+ va_fini = sva + PAGE_SIZE;
+
if (pmap_remove_pte(pmap, pte, sva, *pde)) {
- sva += PAGE_SIZE;
+ /* Entire PT removed and TLBs shot down. */
+ need_tlb_shootdown = false;
break;
+ } else {
+ need_tlb_shootdown = true;
}
}
- if (va != va_next)
- pmap_invalidate_range(pmap, va, sva);
+ if (need_tlb_shootdown)
+ pmap_invalidate_range(pmap, va_init, va_fini);
}
out:
rw_wunlock(&pvh_global_lock);
@@ -1900,10 +1970,11 @@ pmap_remove_all(vm_page_t m)
__func__, (void *)pv->pv_va, (uintmax_t)tpte));
vm_page_dirty(m);
}
- pmap_invalidate_page(pmap, pv->pv_va);
+ if (!pmap_unuse_pt(pmap, pv->pv_va, *pde))
+ pmap_invalidate_page(pmap, pv->pv_va);
+
TAILQ_REMOVE(&m->md.pv_list, pv, pv_list);
- pmap_unuse_pt(pmap, pv->pv_va, *pde);
free_pv_entry(pmap, pv);
PMAP_UNLOCK(pmap);
}
@@ -2810,7 +2881,12 @@ pmap_remove_pages(pmap_t pmap)
TAILQ_REMOVE(&m->md.pv_list, pv, pv_list);
if (TAILQ_EMPTY(&m->md.pv_list))
vm_page_aflag_clear(m, PGA_WRITEABLE);
- pmap_unuse_pt(pmap, pv->pv_va, *pde);
+
+ /*
+ * For simplicity, unconditionally call
+ * pmap_invalidate_all(), below.
+ */
+ (void)pmap_unuse_pt(pmap, pv->pv_va, *pde);
}
}
if (allfree) {
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