svn commit: r196318 - head/sys/amd64/amd64
Konstantin Belousov
kib at FreeBSD.org
Mon Aug 17 13:27:56 UTC 2009
Author: kib
Date: Mon Aug 17 13:27:55 2009
New Revision: 196318
URL: http://svn.freebsd.org/changeset/base/196318
Log:
Correct a critical accounting error in pmap_demote_pde(). Specifically,
when pmap_demote_pde() allocates a page table page to implement a
user-space demotion, it must increment the pmap's resident page count.
Not doing so, can lead to an underflow during address space termination
that causes pmap_remove() to exit prematurely, before it has destroyed
all of the mappings within the specified range. The ultimate effect or
symptom of this error is an assertion failure in vm_page_free_toq()
because the page being freed is still mapped.
This error is only possible when superpage promotion is enabled. Thus,
it only affects FreeBSD versions greater than 7.2.
Tested by: pho, alc
Reviewed by: alc
Approved by: re (rwatson)
MFC after: 1 week
Modified:
head/sys/amd64/amd64/pmap.c
Modified: head/sys/amd64/amd64/pmap.c
==============================================================================
--- head/sys/amd64/amd64/pmap.c Mon Aug 17 13:00:32 2009 (r196317)
+++ head/sys/amd64/amd64/pmap.c Mon Aug 17 13:27:55 2009 (r196318)
@@ -2261,6 +2261,8 @@ pmap_demote_pde(pmap_t pmap, pd_entry_t
" in pmap %p", va, pmap);
return (FALSE);
}
+ if (va < VM_MAXUSER_ADDRESS)
+ pmap->pm_stats.resident_count++;
}
mptepa = VM_PAGE_TO_PHYS(mpte);
firstpte = (pt_entry_t *)PHYS_TO_DMAP(mptepa);
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