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Correct a long-standing error in _pmap_unwire_pte_hold() affecting

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multiprocessors.  Specifically, the error is conditioning the call to
pmap_invalidate_page() on whether the pmap is active on the current CPU.
This call must be unconditional.  Regardless of whether the pmap is active
on the CPU performing _pmap_unwire_pte_hold(), it could be active on another
CPU.  For example, a call to pmap_remove_all() by the page daemon could
result in a call to _pmap_unwire_pte_hold() with the pmap inactive on the
current CPU and active on another CPU.  In such circumstances, failing to
call pmap_invalidate_page() results in a stale TLB entry on the other CPU
that still maps the now deallocated page table page.  What happens next is
typically a mysterious panic in pmap_enter() by the other CPU, either
"pmap_enter: attempted pmap_enter on 4MB page" or "pmap_enter: pte vanished,
va: 0x%lx".  Both occur because the former page table page has been recycled
and allocated to a new purpose.  Consequently, it no longer contains zeroes.

See also Peter's i386/i386/pmap.c revision 1.448 and the related e-mail
thread last year.

Many thanks to the engineers at Sandvine for providing clear and concise
information until all of the pieces of the puzzle fell into place and
for testing an earlier patch.

MT5 Candidate
This commit is contained in:
alc 2004-09-22 05:01:48 +00:00
parent 5015e1ce1f
commit a6bec8ad06
2 changed files with 11 additions and 17 deletions
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13
sys/amd64/amd64/pmap.c
View File

@ -1014,13 +1014,12 @@ _pmap_unwire_pte_hold(pmap_t pmap, vm_offset_t va, vm_page_t m)
pdppg = PHYS_TO_VM_PAGE(*pmap_pml4e(pmap, va) & PG_FRAME);
pmap_unwire_pte_hold(pmap, va, pdppg);
}
if (pmap_is_current(pmap)) {
/*
* Do an invltlb to make the invalidated mapping
* take effect immediately.
*/
pmap_invalidate_page(pmap, pteva);
}
/*
* Do an invltlb to make the invalidated mapping
* take effect immediately.
*/
pmap_invalidate_page(pmap, pteva);
vm_page_free_zero(m);
atomic_subtract_int(&cnt.v_wire_count, 1);

15
sys/i386/i386/pmap.c
View File

@ -1030,18 +1030,13 @@ _pmap_unwire_pte_hold(pmap_t pmap, vm_page_t m)
*/
pmap->pm_pdir[m->pindex] = 0;
--pmap->pm_stats.resident_count;
/*
* We never unwire a kernel page table page, making a
* check for the kernel_pmap unnecessary.
* Do an invltlb to make the invalidated mapping
* take effect immediately.
*/
if ((pmap->pm_pdir[PTDPTDI] & PG_FRAME) == (PTDpde[0] & PG_FRAME)) {
/*
* Do an invltlb to make the invalidated mapping
* take effect immediately.
*/
pteva = VM_MAXUSER_ADDRESS + i386_ptob(m->pindex);
pmap_invalidate_page(pmap, pteva);
}
pteva = VM_MAXUSER_ADDRESS + i386_ptob(m->pindex);
pmap_invalidate_page(pmap, pteva);
vm_page_free_zero(m);
atomic_subtract_int(&cnt.v_wire_count, 1);