0ac52dd766
We need to have irqs disabled to handle all the possible parallel update for
linux page table without holding locks.
Events that we are intersted in while walking page tables are
1) Page fault
2) umap
3) THP split
4) THP collapse
A) local_irq_disabled:
------------------------
1) page fault:
A none to valid transition via page fault is not an issue because we
would either see a none or valid. If it is none, we would error out
the page table walk. We may need to use on stack values when checking for
type of page table elements, because if we do
if (!is_hugepd()) {
if (!pmd_none() {
if (pmd_bad() {
We could take that bad condition because the pmd got converted to a hugepd
after the !is_hugepd check via a hugetlb fault.
The right way would be to check for pmd_none higher up or use on stack value.
2) A valid to none conversion via unmap:
We can safely walk the upper level table, because we don't remove the the
page table entries until rcu grace period. So even if we followed a
wrong pointer we still have the pointer valid till the grace period.
A PTE pointer returned need to be atomically checked for _PAGE_PRESENT and
_PAGE_BUSY. A valid pointer returned could becoming none later. To prevent
pte_clear we take _PAGE_BUSY.
3) THP split:
A valid transparent hugepage is converted to nomal page. Before we split we
do pmd_splitting_flush, which sets the hugepage PTE to _PAGE_SPLITTING
So when walking page table we need to check for pmd_trans_splitting and
handle that. The pte returned should also need to be checked for
_PAGE_SPLITTING before setting _PAGE_BUSY similar to _PAGE_PRESENT. We save
the value of PTE on stack and check for the flag in the local pte value.
If we don't have the value set we can safely operate on the local pte value
and we atomicaly set _PAGE_BUSY.
4) THP collapse:
A normal page gets converted to hugepage. In the collapse path, we
mark the pmd none early (pmdp_clear_flush). With irq disabled, if we
are aleady walking page table we would see the pmd_none and won't continue.
If we see a valid PMD, we should still check for _PAGE_PRESENT before
setting _PAGE_BUSY, to make sure we didn't collapse the PTE to a Huge PTE.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
176 lines
4.8 KiB
C
176 lines
4.8 KiB
C
/*
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* Copyright IBM Corporation, 2013
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* Author Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of version 2.1 of the GNU Lesser General Public License
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it would be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*
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*/
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/*
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* PPC64 THP Support for hash based MMUs
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*/
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#include <linux/mm.h>
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#include <asm/machdep.h>
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int __hash_page_thp(unsigned long ea, unsigned long access, unsigned long vsid,
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pmd_t *pmdp, unsigned long trap, int local, int ssize,
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unsigned int psize)
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{
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unsigned int index, valid;
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unsigned char *hpte_slot_array;
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unsigned long rflags, pa, hidx;
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unsigned long old_pmd, new_pmd;
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int ret, lpsize = MMU_PAGE_16M;
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unsigned long vpn, hash, shift, slot;
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/*
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* atomically mark the linux large page PMD busy and dirty
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*/
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do {
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old_pmd = pmd_val(*pmdp);
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/* If PMD busy, retry the access */
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if (unlikely(old_pmd & _PAGE_BUSY))
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return 0;
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/* If PMD is trans splitting retry the access */
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if (unlikely(old_pmd & _PAGE_SPLITTING))
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return 0;
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/* If PMD permissions don't match, take page fault */
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if (unlikely(access & ~old_pmd))
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return 1;
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/*
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* Try to lock the PTE, add ACCESSED and DIRTY if it was
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* a write access
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*/
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new_pmd = old_pmd | _PAGE_BUSY | _PAGE_ACCESSED;
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if (access & _PAGE_RW)
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new_pmd |= _PAGE_DIRTY;
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} while (old_pmd != __cmpxchg_u64((unsigned long *)pmdp,
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old_pmd, new_pmd));
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/*
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* PP bits. _PAGE_USER is already PP bit 0x2, so we only
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* need to add in 0x1 if it's a read-only user page
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*/
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rflags = new_pmd & _PAGE_USER;
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if ((new_pmd & _PAGE_USER) && !((new_pmd & _PAGE_RW) &&
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(new_pmd & _PAGE_DIRTY)))
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rflags |= 0x1;
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/*
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* _PAGE_EXEC -> HW_NO_EXEC since it's inverted
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*/
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rflags |= ((new_pmd & _PAGE_EXEC) ? 0 : HPTE_R_N);
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#if 0
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if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) {
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/*
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* No CPU has hugepages but lacks no execute, so we
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* don't need to worry about that case
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*/
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rflags = hash_page_do_lazy_icache(rflags, __pte(old_pte), trap);
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}
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#endif
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/*
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* Find the slot index details for this ea, using base page size.
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*/
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shift = mmu_psize_defs[psize].shift;
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index = (ea & ~HPAGE_PMD_MASK) >> shift;
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BUG_ON(index >= 4096);
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vpn = hpt_vpn(ea, vsid, ssize);
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hash = hpt_hash(vpn, shift, ssize);
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hpte_slot_array = get_hpte_slot_array(pmdp);
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valid = hpte_valid(hpte_slot_array, index);
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if (valid) {
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/* update the hpte bits */
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hidx = hpte_hash_index(hpte_slot_array, index);
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if (hidx & _PTEIDX_SECONDARY)
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hash = ~hash;
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slot = (hash & htab_hash_mask) * HPTES_PER_GROUP;
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slot += hidx & _PTEIDX_GROUP_IX;
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ret = ppc_md.hpte_updatepp(slot, rflags, vpn,
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psize, lpsize, ssize, local);
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/*
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* We failed to update, try to insert a new entry.
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*/
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if (ret == -1) {
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/*
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* large pte is marked busy, so we can be sure
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* nobody is looking at hpte_slot_array. hence we can
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* safely update this here.
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*/
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valid = 0;
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new_pmd &= ~_PAGE_HPTEFLAGS;
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hpte_slot_array[index] = 0;
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} else
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/* clear the busy bits and set the hash pte bits */
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new_pmd = (new_pmd & ~_PAGE_HPTEFLAGS) | _PAGE_HASHPTE;
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}
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if (!valid) {
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unsigned long hpte_group;
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/* insert new entry */
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pa = pmd_pfn(__pmd(old_pmd)) << PAGE_SHIFT;
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repeat:
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hpte_group = ((hash & htab_hash_mask) * HPTES_PER_GROUP) & ~0x7UL;
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/* clear the busy bits and set the hash pte bits */
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new_pmd = (new_pmd & ~_PAGE_HPTEFLAGS) | _PAGE_HASHPTE;
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/* Add in WIMG bits */
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rflags |= (new_pmd & (_PAGE_WRITETHRU | _PAGE_NO_CACHE |
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_PAGE_COHERENT | _PAGE_GUARDED));
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/* Insert into the hash table, primary slot */
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slot = ppc_md.hpte_insert(hpte_group, vpn, pa, rflags, 0,
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psize, lpsize, ssize);
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/*
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* Primary is full, try the secondary
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*/
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if (unlikely(slot == -1)) {
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hpte_group = ((~hash & htab_hash_mask) *
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HPTES_PER_GROUP) & ~0x7UL;
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slot = ppc_md.hpte_insert(hpte_group, vpn, pa,
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rflags, HPTE_V_SECONDARY,
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psize, lpsize, ssize);
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if (slot == -1) {
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if (mftb() & 0x1)
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hpte_group = ((hash & htab_hash_mask) *
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HPTES_PER_GROUP) & ~0x7UL;
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ppc_md.hpte_remove(hpte_group);
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goto repeat;
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}
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}
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/*
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* Hypervisor failure. Restore old pmd and return -1
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* similar to __hash_page_*
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*/
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if (unlikely(slot == -2)) {
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*pmdp = __pmd(old_pmd);
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hash_failure_debug(ea, access, vsid, trap, ssize,
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psize, lpsize, old_pmd);
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return -1;
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}
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/*
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* large pte is marked busy, so we can be sure
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* nobody is looking at hpte_slot_array. hence we can
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* safely update this here.
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*/
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mark_hpte_slot_valid(hpte_slot_array, index, slot);
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}
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/*
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* No need to use ldarx/stdcx here
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*/
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*pmdp = __pmd(new_pmd & ~_PAGE_BUSY);
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return 0;
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}
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