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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2015-03-30 08:11:03 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2015-04-17 04:23:39 +0300
commit691e95fd7396905a38d98919e9c150dbc3ea21a3 (patch)
treed89b898d4f42d167f0da169f482d7104b46870d8 /arch/powerpc/perf
parentdac5657067919161eb3273ca787d8ae9814801e7 (diff)
downloadlinux-691e95fd7396905a38d98919e9c150dbc3ea21a3.tar.xz
powerpc/mm/thp: Make page table walk safe against thp split/collapse
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>
Diffstat (limited to 'arch/powerpc/perf')
-rw-r--r--arch/powerpc/perf/callchain.c24
1 files changed, 14 insertions, 10 deletions
diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
index ead55351b254..ff09cde20cd2 100644
--- a/arch/powerpc/perf/callchain.c
+++ b/arch/powerpc/perf/callchain.c
@@ -111,41 +111,45 @@ perf_callchain_kernel(struct perf_callchain_entry *entry, struct pt_regs *regs)
* interrupt context, so if the access faults, we read the page tables
* to find which page (if any) is mapped and access it directly.
*/
-static int read_user_stack_slow(void __user *ptr, void *ret, int nb)
+static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
{
+ int ret = -EFAULT;
pgd_t *pgdir;
pte_t *ptep, pte;
unsigned shift;
unsigned long addr = (unsigned long) ptr;
unsigned long offset;
- unsigned long pfn;
+ unsigned long pfn, flags;
void *kaddr;
pgdir = current->mm->pgd;
if (!pgdir)
return -EFAULT;
+ local_irq_save(flags);
ptep = find_linux_pte_or_hugepte(pgdir, addr, &shift);
+ if (!ptep)
+ goto err_out;
if (!shift)
shift = PAGE_SHIFT;
/* align address to page boundary */
offset = addr & ((1UL << shift) - 1);
- addr -= offset;
- if (ptep == NULL)
- return -EFAULT;
- pte = *ptep;
+ pte = READ_ONCE(*ptep);
if (!pte_present(pte) || !(pte_val(pte) & _PAGE_USER))
- return -EFAULT;
+ goto err_out;
pfn = pte_pfn(pte);
if (!page_is_ram(pfn))
- return -EFAULT;
+ goto err_out;
/* no highmem to worry about here */
kaddr = pfn_to_kaddr(pfn);
- memcpy(ret, kaddr + offset, nb);
- return 0;
+ memcpy(buf, kaddr + offset, nb);
+ ret = 0;
+err_out:
+ local_irq_restore(flags);
+ return ret;
}
static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)