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Because of AArch64's weak memory consistency model, we need to include a

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memory barrier between the stores for initializing a page table page and
the store for adding that page to the page table.  Otherwise, a page table
walk by another processor's MMU could see the page table page before it
sees the initialized entries.

Simplify pmap_growkernel().  In particular, eliminate an unnecessary TLB
invalidation.

Reviewed by:	andrew, markj
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D21126
This commit is contained in:
Alan Cox 2019-08-02 22:36:42 +00:00
parent 60f2e2e702
commit 072a067fb8
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=350546
1 changed files with 20 additions and 3 deletions
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23
sys/arm64/arm64/pmap.c
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@ -1524,6 +1524,16 @@ _pmap_alloc_l3(pmap_t pmap, vm_pindex_t ptepindex, struct rwlock **lockp)
if ((m->flags & PG_ZERO) == 0)
pmap_zero_page(m);
/*
* Because of AArch64's weak memory consistency model, we must have a
* barrier here to ensure that the stores for zeroing "m", whether by
* pmap_zero_page() or an earlier function, are visible before adding
* "m" to the page table. Otherwise, a page table walk by another
* processor's MMU could see the mapping to "m" and a stale, non-zero
* PTE within "m".
*/
dmb(ishst);
/*
* Map the pagetable page into the process address space, if
* it isn't already there.
@ -1775,12 +1785,14 @@ pmap_growkernel(vm_offset_t addr)
panic("pmap_growkernel: no memory to grow kernel");
if ((nkpg->flags & PG_ZERO) == 0)
pmap_zero_page(nkpg);
/* See the dmb() in _pmap_alloc_l3(). */
dmb(ishst);
paddr = VM_PAGE_TO_PHYS(nkpg);
pmap_store(l1, paddr | L1_TABLE);
continue; /* try again */
}
l2 = pmap_l1_to_l2(l1, kernel_vm_end);
if ((pmap_load(l2) & ATTR_AF) != 0) {
if (pmap_load(l2) != 0) {
kernel_vm_end = (kernel_vm_end + L2_SIZE) & ~L2_OFFSET;
if (kernel_vm_end - 1 >= vm_map_max(kernel_map)) {
kernel_vm_end = vm_map_max(kernel_map);
@ -1796,9 +1808,10 @@ pmap_growkernel(vm_offset_t addr)
panic("pmap_growkernel: no memory to grow kernel");
if ((nkpg->flags & PG_ZERO) == 0)
pmap_zero_page(nkpg);
/* See the dmb() in _pmap_alloc_l3(). */
dmb(ishst);
paddr = VM_PAGE_TO_PHYS(nkpg);
pmap_load_store(l2, paddr | L2_TABLE);
pmap_invalidate_page(kernel_pmap, kernel_vm_end);
pmap_store(l2, paddr | L2_TABLE);
kernel_vm_end = (kernel_vm_end + L2_SIZE) & ~L2_OFFSET;
if (kernel_vm_end - 1 >= vm_map_max(kernel_map)) {
@ -5531,6 +5544,10 @@ pmap_demote_l2_locked(pmap_t pmap, pt_entry_t *l2, vm_offset_t va,
/*
* If the page table page is not leftover from an earlier promotion,
* or the mapping attributes have changed, (re)initialize the L3 table.
*
* When pmap_update_entry() clears the old L2 mapping, it (indirectly)
* performs a dsb(). That dsb() ensures that the stores for filling
* "l3" are visible before "l3" is added to the page table.
*/
if (ml3->valid == 0 || (l3[0] & ATTR_MASK) != (newl3 & ATTR_MASK))
pmap_fill_l3(l3, newl3);