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If vm_map_find() is asked to allocate a superpage-aligned region of virtual

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addresses that is greater than a superpage in size but not a multiple of
the superpage size, then vm_map_find() is not always expanding the kernel
pmap to support the last few small pages being allocated.  These failures
are not commonplace, so this was first noticed by someone porting FreeBSD
to a new architecture.  Previously, we grew the kernel page table in
vm_map_findspace() when we found the first available virtual address.
This works most of the time because we always grow the kernel pmap or page
table by an amount that is a multiple of the superpage size.  Now, instead,
we defer the call to pmap_growkernel() until we are committed to a range
of virtual addresses in vm_map_insert().  In general, there is another
reason to prefer calling pmap_growkernel() in vm_map_insert().  It makes
it possible for someone to do the equivalent of an mmap(MAP_FIXED) on the
kernel map.

Reported by:	Svatopluk Kraus
Reviewed by:	kib@
MFC after:	3 weeks
This commit is contained in:
Alan Cox 2010-10-04 16:49:40 +00:00
parent 94363f5311
commit f8616ebfae
1 changed files with 8 additions and 14 deletions
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22
sys/vm/vm_map.c
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@ -1163,6 +1163,9 @@ vm_map_insert(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
}
charged:
/* Expand the kernel pmap, if necessary. */
if (map == kernel_map && end > kernel_vm_end)
pmap_growkernel(end);
if (object != NULL) {
/*
* OBJ_ONEMAPPING must be cleared unless this mapping
@ -1299,7 +1302,7 @@ vm_map_findspace(vm_map_t map, vm_offset_t start, vm_size_t length,
vm_offset_t *addr) /* OUT */
{
vm_map_entry_t entry;
vm_offset_t end, st;
vm_offset_t st;
/*
* Request must fit within min/max VM address and must avoid
@ -1313,7 +1316,7 @@ vm_map_findspace(vm_map_t map, vm_offset_t start, vm_size_t length,
/* Empty tree means wide open address space. */
if (map->root == NULL) {
*addr = start;
goto found;
return (0);
}
/*
@ -1323,7 +1326,7 @@ vm_map_findspace(vm_map_t map, vm_offset_t start, vm_size_t length,
map->root = vm_map_entry_splay(start, map->root);
if (start + length <= map->root->start) {
*addr = start;
goto found;
return (0);
}
/*
@ -1334,7 +1337,7 @@ vm_map_findspace(vm_map_t map, vm_offset_t start, vm_size_t length,
st = (start > map->root->end) ? start : map->root->end;
if (length <= map->root->end + map->root->adj_free - st) {
*addr = st;
goto found;
return (0);
}
/* With max_free, can immediately tell if no solution. */
@ -1352,22 +1355,13 @@ vm_map_findspace(vm_map_t map, vm_offset_t start, vm_size_t length,
entry = entry->left;
else if (entry->adj_free >= length) {
*addr = entry->end;
goto found;
return (0);
} else
entry = entry->right;
}
/* Can't get here, so panic if we do. */
panic("vm_map_findspace: max_free corrupt");
found:
/* Expand the kernel pmap, if necessary. */
if (map == kernel_map) {
end = round_page(*addr + length);
if (end > kernel_vm_end)
pmap_growkernel(end);
}
return (0);
}
int