From: Aneesh Kumar K.V Date: Mon, 30 Mar 2015 05:11:03 +0000 (+0530) Subject: powerpc/mm/thp: Make page table walk safe against thp split/collapse X-Git-Tag: omap-for-v4.1/fixes-rc1~26^2~3 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=691e95fd7396905a38d98919e9c150dbc3ea21a3;p=pandora-kernel.git 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 Signed-off-by: Michael Ellerman --- Reading git-diff-tree failed