• Aneesh Kumar K.V's avatar
    powerpc/mm/thp: Make page table walk safe against thp split/collapse · 691e95fd
    Aneesh Kumar K.V authored
    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: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    691e95fd
eeh.c 44.2 KB