1. 25 Oct, 2012 1 commit
    • Gavin Shan's avatar
      mm/mmu_notifier: allocate mmu_notifier in advance · 35cfa2b0
      Gavin Shan authored
      While allocating mmu_notifier with parameter GFP_KERNEL, swap would start
      to work in case of tight available memory.  Eventually, that would lead to
      a deadlock while the swap deamon swaps anonymous pages.  It was caused by
      commit e0f3c3f7
      
       ("mm/mmu_notifier: init notifier if necessary").
      
        =================================
        [ INFO: inconsistent lock state ]
        3.7.0-rc1+ #518 Not tainted
        ---------------------------------
        inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
        kswapd0/35 [HC0[0]:SC0[0]:HE1:SE1] takes:
         (&mapping->i_mmap_mutex){+.+.?.}, at: page_referenced+0x9c/0x2e0
        {RECLAIM_FS-ON-W} state was registered at:
           mark_held_locks+0x86/0x150
           lockdep_trace_alloc+0x67/0xc0
           kmem_cache_alloc_trace+0x33/0x230
           do_mmu_notifier_register+0x87/0x180
           mmu_notifier_register+0x13/0x20
           kvm_dev_ioctl+0x428/0x510
           do_vfs_ioctl+0x98/0x570
           sys_ioctl+0x91/0xb0
           system_call_fastpath+0x16/0x1b
        irq event stamp: 825
        hardirqs last  enabled at (825): _raw_spin_unlock_irq+0x30/0x60
        hardirqs last disabled at (824): _raw_spin_lock_irq+0x19/0x80
        softirqs last  enabled at (0): copy_process+0x630/0x17c0
        softirqs last disabled at (0): (null)
        ...
      
      Simply back out the above commit, which was a small performance
      optimization.
      
      Signed-off-by: default avatarGavin Shan <shangw@linux.vnet.ibm.com>
      Reported-by: default avatarAndrea Righi <andrea@betterlinux.com>
      Tested-by: default avatarAndrea Righi <andrea@betterlinux.com>
      Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Avi Kivity <avi@redhat.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
      Cc: Sagi Grimberg <sagig@mellanox.co.il>
      Cc: Haggai Eran <haggaie@mellanox.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      35cfa2b0
  2. 09 Oct, 2012 4 commits
  3. 31 Jul, 2012 1 commit
    • Xiao Guangrong's avatar
      mm: mmu_notifier: fix freed page still mapped in secondary MMU · 3ad3d901
      Xiao Guangrong authored
      
      
      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: default avatarXiao 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: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      3ad3d901
  4. 31 Oct, 2011 1 commit
  5. 13 Jan, 2011 1 commit
    • Andrea Arcangeli's avatar
      thp: mmu_notifier_test_young · 8ee53820
      Andrea Arcangeli authored
      
      
      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: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8ee53820
  6. 30 Mar, 2010 1 commit
    • Tejun Heo's avatar
      include cleanup: Update gfp.h and slab.h includes to prepare for breaking... · 5a0e3ad6
      Tejun Heo authored
      include cleanup: Update gfp.h and slab.h includes to prepare for breaking 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: default avatarTejun Heo <tj@kernel.org>
      Guess-its-ok-by: default avatarChristoph Lameter <cl@linux-foundation.org>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
      5a0e3ad6
  7. 22 Sep, 2009 1 commit
    • Izik Eidus's avatar
      ksm: add mmu_notifier set_pte_at_notify() · 828502d3
      Izik Eidus authored
      
      
      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: default avatarIzik Eidus <ieidus@redhat.com>
      Signed-off-by: default avatarChris Wright <chrisw@redhat.com>
      Signed-off-by: default avatarHugh 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: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      828502d3
  8. 28 Jul, 2008 1 commit
    • Andrea Arcangeli's avatar
      mmu-notifiers: core · cddb8a5c
      Andrea Arcangeli authored
      
      
      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: default avatarAndrea Arcangeli <andrea@qumranet.com>
      Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
      Signed-off-by: default avatarChristoph 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: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      cddb8a5c