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Commits on Aug 1, 2012
  1. mm: mmu_notifier: fix freed page still mapped in secondary MMU

    Xiao Guangrong authored committed
    mmu_notifier_release() is called when the process is exiting.  It will
    delete all the mmu notifiers.  But at this time the page belonging to the
    process is still present in page tables and is present on the LRU list, so
    this race will happen:
    
          CPU 0                 CPU 1
    mmu_notifier_release:    try_to_unmap:
       hlist_del_init_rcu(&mn->hlist);
                                ptep_clear_flush_notify:
                                      mmu nofifler not found
                                free page  !!!!!!
                                /*
                                 * At the point, the page has been
                                 * freed, but it is still mapped in
                                 * the secondary MMU.
                                 */
    
      mn->ops->release(mn, mm);
    
    Then the box is not stable and sometimes we can get this bug:
    
    [  738.075923] BUG: Bad page state in process migrate-perf  pfn:03bec
    [  738.075931] page:ffffea00000efb00 count:0 mapcount:0 mapping:          (null) index:0x8076
    [  738.075936] page flags: 0x20000000000014(referenced|dirty)
    
    The same issue is present in mmu_notifier_unregister().
    
    We can call ->release before deleting the notifier to ensure the page has
    been unmapped from the secondary MMU before it is freed.
    
    Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Marcelo Tosatti <mtosatti@redhat.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commits on Oct 31, 2011
  1. @paulgortmaker

    mm: Map most files to use export.h instead of module.h

    paulgortmaker authored
    The files changed within are only using the EXPORT_SYMBOL
    macro variants.  They are not using core modular infrastructure
    and hence don't need module.h but only the export.h header.
    
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Commits on Jan 14, 2011
  1. thp: mmu_notifier_test_young

    Andrea Arcangeli authored committed
    For GRU and EPT, we need gup-fast to set referenced bit too (this is why
    it's correct to return 0 when shadow_access_mask is zero, it requires
    gup-fast to set the referenced bit).  qemu-kvm access already sets the
    young bit in the pte if it isn't zero-copy, if it's zero copy or a shadow
    paging EPT minor fault we relay on gup-fast to signal the page is in
    use...
    
    We also need to check the young bits on the secondary pagetables for NPT
    and not nested shadow mmu as the data may never get accessed again by the
    primary pte.
    
    Without this closer accuracy, we'd have to remove the heuristic that
    avoids collapsing hugepages in hugepage virtual regions that have not even
    a single subpage in use.
    
    ->test_young is full backwards compatible with GRU and other usages that
    don't have young bits in pagetables set by the hardware and that should
    nuke the secondary mmu mappings when ->clear_flush_young runs just like
    EPT does.
    
    Removing the heuristic that checks the young bit in
    khugepaged/collapse_huge_page completely isn't so bad either probably but
    I thought it was worth it and this makes it reliable.
    
    Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commits on Mar 30, 2010
  1. include cleanup: Update gfp.h and slab.h includes to prepare for brea…

    Tejun Heo authored
    …king implicit slab.h inclusion from percpu.h
    
    percpu.h is included by sched.h and module.h and thus ends up being
    included when building most .c files.  percpu.h includes slab.h which
    in turn includes gfp.h making everything defined by the two files
    universally available and complicating inclusion dependencies.
    
    percpu.h -> slab.h dependency is about to be removed.  Prepare for
    this change by updating users of gfp and slab facilities include those
    headers directly instead of assuming availability.  As this conversion
    needs to touch large number of source files, the following script is
    used as the basis of conversion.
    
      http://userweb.kernel.org/~tj/misc/slabh-sweep.py
    
    The script does the followings.
    
    * Scan files for gfp and slab usages and update includes such that
      only the necessary includes are there.  ie. if only gfp is used,
      gfp.h, if slab is used, slab.h.
    
    * When the script inserts a new include, it looks at the include
      blocks and try to put the new include such that its order conforms
      to its surrounding.  It's put in the include block which contains
      core kernel includes, in the same order that the rest are ordered -
      alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
      doesn't seem to be any matching order.
    
    * If the script can't find a place to put a new include (mostly
      because the file doesn't have fitting include block), it prints out
      an error message indicating which .h file needs to be added to the
      file.
    
    The conversion was done in the following steps.
    
    1. The initial automatic conversion of all .c files updated slightly
       over 4000 files, deleting around 700 includes and adding ~480 gfp.h
       and ~3000 slab.h inclusions.  The script emitted errors for ~400
       files.
    
    2. Each error was manually checked.  Some didn't need the inclusion,
       some needed manual addition while adding it to implementation .h or
       embedding .c file was more appropriate for others.  This step added
       inclusions to around 150 files.
    
    3. The script was run again and the output was compared to the edits
       from #2 to make sure no file was left behind.
    
    4. Several build tests were done and a couple of problems were fixed.
       e.g. lib/decompress_*.c used malloc/free() wrappers around slab
       APIs requiring slab.h to be added manually.
    
    5. The script was run on all .h files but without automatically
       editing them as sprinkling gfp.h and slab.h inclusions around .h
       files could easily lead to inclusion dependency hell.  Most gfp.h
       inclusion directives were ignored as stuff from gfp.h was usually
       wildly available and often used in preprocessor macros.  Each
       slab.h inclusion directive was examined and added manually as
       necessary.
    
    6. percpu.h was updated not to include slab.h.
    
    7. Build test were done on the following configurations and failures
       were fixed.  CONFIG_GCOV_KERNEL was turned off for all tests (as my
       distributed build env didn't work with gcov compiles) and a few
       more options had to be turned off depending on archs to make things
       build (like ipr on powerpc/64 which failed due to missing writeq).
    
       * x86 and x86_64 UP and SMP allmodconfig and a custom test config.
       * powerpc and powerpc64 SMP allmodconfig
       * sparc and sparc64 SMP allmodconfig
       * ia64 SMP allmodconfig
       * s390 SMP allmodconfig
       * alpha SMP allmodconfig
       * um on x86_64 SMP allmodconfig
    
    8. percpu.h modifications were reverted so that it could be applied as
       a separate patch and serve as bisection point.
    
    Given the fact that I had only a couple of failures from tests on step
    6, I'm fairly confident about the coverage of this conversion patch.
    If there is a breakage, it's likely to be something in one of the arch
    headers which should be easily discoverable easily on most builds of
    the specific arch.
    
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Commits on Sep 22, 2009
  1. ksm: add mmu_notifier set_pte_at_notify()

    Izik Eidus authored committed
    KSM is a linux driver that allows dynamicly sharing identical memory pages
    between one or more processes.
    
    Unlike tradtional page sharing that is made at the allocation of the
    memory, ksm do it dynamicly after the memory was created.  Memory is
    periodically scanned; identical pages are identified and merged.
    
    The sharing is made in a transparent way to the processes that use it.
    
    Ksm is highly important for hypervisors (kvm), where in production
    enviorments there might be many copys of the same data data among the host
    memory.  This kind of data can be: similar kernels, librarys, cache, and
    so on.
    
    Even that ksm was wrote for kvm, any userspace application that want to
    use it to share its data can try it.
    
    Ksm may be useful for any application that might have similar (page
    aligment) data strctures among the memory, ksm will find this data merge
    it to one copy, and even if it will be changed and thereforew copy on
    writed, ksm will merge it again as soon as it will be identical again.
    
    Another reason to consider using ksm is the fact that it might simplify
    alot the userspace code of application that want to use shared private
    data, instead that the application will mange shared area, ksm will do
    this for the application, and even write to this data will be allowed
    without any synchinization acts from the application.
    
    Ksm was designed to be a loadable module that doesn't change the VM code
    of linux.
    
    This patch:
    
    The set_pte_at_notify() macro allows setting a pte in the shadow page
    table directly, instead of flushing the shadow page table entry and then
    getting vmexit to set it.  It uses a new change_pte() callback to do so.
    
    set_pte_at_notify() is an optimization for kvm, and other users of
    mmu_notifiers, for COW pages.  It is useful for kvm when ksm is used,
    because it allows kvm not to have to receive vmexit and only then map the
    ksm page into the shadow page table, but instead map it directly at the
    same time as Linux maps the page into the host page table.
    
    Users of mmu_notifiers who don't implement new mmu_notifier_change_pte()
    callback will just receive the mmu_notifier_invalidate_page() callback.
    
    Signed-off-by: Izik Eidus <ieidus@redhat.com>
    Signed-off-by: Chris Wright <chrisw@redhat.com>
    Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Cc: Balbir Singh <balbir@in.ibm.com>
    Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commits on Jul 28, 2008
  1. mmu-notifiers: core

    Andrea Arcangeli authored committed
    With KVM/GFP/XPMEM there isn't just the primary CPU MMU pointing to pages.
     There are secondary MMUs (with secondary sptes and secondary tlbs) too.
    sptes in the kvm case are shadow pagetables, but when I say spte in
    mmu-notifier context, I mean "secondary pte".  In GRU case there's no
    actual secondary pte and there's only a secondary tlb because the GRU
    secondary MMU has no knowledge about sptes and every secondary tlb miss
    event in the MMU always generates a page fault that has to be resolved by
    the CPU (this is not the case of KVM where the a secondary tlb miss will
    walk sptes in hardware and it will refill the secondary tlb transparently
    to software if the corresponding spte is present).  The same way
    zap_page_range has to invalidate the pte before freeing the page, the spte
    (and secondary tlb) must also be invalidated before any page is freed and
    reused.
    
    Currently we take a page_count pin on every page mapped by sptes, but that
    means the pages can't be swapped whenever they're mapped by any spte
    because they're part of the guest working set.  Furthermore a spte unmap
    event can immediately lead to a page to be freed when the pin is released
    (so requiring the same complex and relatively slow tlb_gather smp safe
    logic we have in zap_page_range and that can be avoided completely if the
    spte unmap event doesn't require an unpin of the page previously mapped in
    the secondary MMU).
    
    The mmu notifiers allow kvm/GRU/XPMEM to attach to the tsk->mm and know
    when the VM is swapping or freeing or doing anything on the primary MMU so
    that the secondary MMU code can drop sptes before the pages are freed,
    avoiding all page pinning and allowing 100% reliable swapping of guest
    physical address space.  Furthermore it avoids the code that teardown the
    mappings of the secondary MMU, to implement a logic like tlb_gather in
    zap_page_range that would require many IPI to flush other cpu tlbs, for
    each fixed number of spte unmapped.
    
    To make an example: if what happens on the primary MMU is a protection
    downgrade (from writeable to wrprotect) the secondary MMU mappings will be
    invalidated, and the next secondary-mmu-page-fault will call
    get_user_pages and trigger a do_wp_page through get_user_pages if it
    called get_user_pages with write=1, and it'll re-establishing an updated
    spte or secondary-tlb-mapping on the copied page.  Or it will setup a
    readonly spte or readonly tlb mapping if it's a guest-read, if it calls
    get_user_pages with write=0.  This is just an example.
    
    This allows to map any page pointed by any pte (and in turn visible in the
    primary CPU MMU), into a secondary MMU (be it a pure tlb like GRU, or an
    full MMU with both sptes and secondary-tlb like the shadow-pagetable layer
    with kvm), or a remote DMA in software like XPMEM (hence needing of
    schedule in XPMEM code to send the invalidate to the remote node, while no
    need to schedule in kvm/gru as it's an immediate event like invalidating
    primary-mmu pte).
    
    At least for KVM without this patch it's impossible to swap guests
    reliably.  And having this feature and removing the page pin allows
    several other optimizations that simplify life considerably.
    
    Dependencies:
    
    1) mm_take_all_locks() to register the mmu notifier when the whole VM
       isn't doing anything with "mm".  This allows mmu notifier users to keep
       track if the VM is in the middle of the invalidate_range_begin/end
       critical section with an atomic counter incraese in range_begin and
       decreased in range_end.  No secondary MMU page fault is allowed to map
       any spte or secondary tlb reference, while the VM is in the middle of
       range_begin/end as any page returned by get_user_pages in that critical
       section could later immediately be freed without any further
       ->invalidate_page notification (invalidate_range_begin/end works on
       ranges and ->invalidate_page isn't called immediately before freeing
       the page).  To stop all page freeing and pagetable overwrites the
       mmap_sem must be taken in write mode and all other anon_vma/i_mmap
       locks must be taken too.
    
    2) It'd be a waste to add branches in the VM if nobody could possibly
       run KVM/GRU/XPMEM on the kernel, so mmu notifiers will only enabled if
       CONFIG_KVM=m/y.  In the current kernel kvm won't yet take advantage of
       mmu notifiers, but this already allows to compile a KVM external module
       against a kernel with mmu notifiers enabled and from the next pull from
       kvm.git we'll start using them.  And GRU/XPMEM will also be able to
       continue the development by enabling KVM=m in their config, until they
       submit all GRU/XPMEM GPLv2 code to the mainline kernel.  Then they can
       also enable MMU_NOTIFIERS in the same way KVM does it (even if KVM=n).
       This guarantees nobody selects MMU_NOTIFIER=y if KVM and GRU and XPMEM
       are all =n.
    
    The mmu_notifier_register call can fail because mm_take_all_locks may be
    interrupted by a signal and return -EINTR.  Because mmu_notifier_reigster
    is used when a driver startup, a failure can be gracefully handled.  Here
    an example of the change applied to kvm to register the mmu notifiers.
    Usually when a driver startups other allocations are required anyway and
    -ENOMEM failure paths exists already.
    
     struct  kvm *kvm_arch_create_vm(void)
     {
            struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
    +       int err;
    
            if (!kvm)
                    return ERR_PTR(-ENOMEM);
    
            INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
    
    +       kvm->arch.mmu_notifier.ops = &kvm_mmu_notifier_ops;
    +       err = mmu_notifier_register(&kvm->arch.mmu_notifier, current->mm);
    +       if (err) {
    +               kfree(kvm);
    +               return ERR_PTR(err);
    +       }
    +
            return kvm;
     }
    
    mmu_notifier_unregister returns void and it's reliable.
    
    The patch also adds a few needed but missing includes that would prevent
    kernel to compile after these changes on non-x86 archs (x86 didn't need
    them by luck).
    
    [akpm@linux-foundation.org: coding-style fixes]
    [akpm@linux-foundation.org: fix mm/filemap_xip.c build]
    [akpm@linux-foundation.org: fix mm/mmu_notifier.c build]
    Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
    Signed-off-by: Nick Piggin <npiggin@suse.de>
    Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
    Cc: Jack Steiner <steiner@sgi.com>
    Cc: Robin Holt <holt@sgi.com>
    Cc: Nick Piggin <npiggin@suse.de>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Kanoj Sarcar <kanojsarcar@yahoo.com>
    Cc: Roland Dreier <rdreier@cisco.com>
    Cc: Steve Wise <swise@opengridcomputing.com>
    Cc: Avi Kivity <avi@qumranet.com>
    Cc: Hugh Dickins <hugh@veritas.com>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Anthony Liguori <aliguori@us.ibm.com>
    Cc: Chris Wright <chrisw@redhat.com>
    Cc: Marcelo Tosatti <marcelo@kvack.org>
    Cc: Eric Dumazet <dada1@cosmosbay.com>
    Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
    Cc: Izik Eidus <izike@qumranet.com>
    Cc: Anthony Liguori <aliguori@us.ibm.com>
    Cc: Rik van Riel <riel@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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