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When pmap_change_attr() changes the PAT setting on a kernel mapping, it has

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to simultaneously change the PAT setting for the same pages within the
direct map region.  This may require the demotion of a 2MB page mapping and
the allocation of a page table page.  This revision gives the highest
possible priority (VM_ALLOC_INTERRUPT) to this page allocation, so that
pmap_change_attr() is less likely to fail.  (In general, kernel page table
page allocations have the highest priority, so this is not creating a new
precedent.)

(Demotion of 1GB page mappings within the direct map already specifies
VM_ALLOC_INTERRUPT to vm_page_alloc(), so only pmap_demote_pde() must be
changed.)

Approved by:	re (kib)
This commit is contained in:
Alan Cox 2009-07-06 18:43:42 +00:00
parent 0d0a6650d7
commit 133898afd5
1 changed files with 11 additions and 3 deletions
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14
sys/amd64/amd64/pmap.c
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@ -2218,11 +2218,19 @@ pmap_demote_pde(pmap_t pmap, pd_entry_t *pde, vm_offset_t va)
/*
* Invalidate the 2MB page mapping and return "failure" if the
* mapping was never accessed or the allocation of the new
* page table page fails.
* page table page fails. If the 2MB page mapping belongs to
* the direct map region of the kernel's address space, then
* the page allocation request specifies the highest possible
* priority (VM_ALLOC_INTERRUPT). Otherwise, the priority is
* normal. Page table pages are preallocated for every other
* part of the kernel address space, so the direct map region
* is the only part of the kernel address space that must be
* handled here.
*/
if ((oldpde & PG_A) == 0 || (mpte = vm_page_alloc(NULL,
pmap_pde_pindex(va), VM_ALLOC_NOOBJ | VM_ALLOC_NORMAL |
VM_ALLOC_WIRED)) == NULL) {
pmap_pde_pindex(va), (va >= DMAP_MIN_ADDRESS && va <
DMAP_MAX_ADDRESS ? VM_ALLOC_INTERRUPT : VM_ALLOC_NORMAL) |
VM_ALLOC_NOOBJ | VM_ALLOC_WIRED)) == NULL) {
free = NULL;
pmap_remove_pde(pmap, pde, trunc_2mpage(va), &free);
pmap_invalidate_page(pmap, trunc_2mpage(va));