xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

powerpc/mm/thp: Make page table walk safe against thp split/collapse

Browse Source 
We can disable a THP split or a hugepage collapse by disabling irq.
We do send IPI to all the cpus in the early part of split/collapse,
and disabling local irq ensure we don't make progress with
split/collapse. If the THP is getting split we return NULL from
find_linux_pte_or_hugepte(). For all the current callers it should be ok.
We need to be careful if we want to use returned pte_t pointer outside
the irq disabled region. W.r.t to THP split, the pfn remains the same,
but then a hugepage collapse will result in a pfn change. There are
few steps we can take to avoid a hugepage collapse.One way is to take page
reference inside the irq disable region. Other option is to take
mmap_sem so that a parallel collapse will not happen. We can also
disable collapse by taking pmd_lock. Another method used by kvm
subsystem is to check whether we had a mmu_notifer update in between
using mmu_notifier_retry().

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Aneesh Kumar K.V
2015-03-30 10:41:03 +05:30
committed by Michael Ellerman
parent dac5657067
commit 691e95fd73
9 changed files with 88 additions and 36 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
arch/powerpc/kvm/e500_mmu_host.c
View File

@@ -338,6 +338,7 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
pte_t *ptep;
unsigned int wimg = 0;
pgd_t *pgdir;
unsigned long flags;
/* used to check for invalidations in progress */
mmu_seq = kvm->mmu_notifier_seq;
@@ -468,14 +469,23 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
pgdir = vcpu_e500->vcpu.arch.pgdir;
/*
* We are just looking at the wimg bits, so we don't
* care much about the trans splitting bit.
* We are holding kvm->mmu_lock so a notifier invalidate
* can't run hence pfn won't change.
*/
local_irq_save(flags);
ptep = find_linux_pte_or_hugepte(pgdir, hva, NULL);
if (ptep) {
pte_t pte = READ_ONCE(*ptep);
if (pte_present(pte))
if (pte_present(pte)) {
wimg = (pte_val(pte) >> PTE_WIMGE_SHIFT) &
MAS2_WIMGE_MASK;
else {
local_irq_restore(flags);
} else {
local_irq_restore(flags);
pr_err_ratelimited("%s: pte not present: gfn %lx,pfn %lx\n",
__func__, (long)gfn, pfn);
ret = -EINVAL;