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  1. Apr 08, 2020
  2. Apr 07, 2020
  3. Apr 02, 2020
    • Peter Xu's avatar
      mm: allow VM_FAULT_RETRY for multiple times · 4064b982
      Peter Xu authored
      The idea comes from a discussion between Linus and Andrea [1].
      
      Before this patch we only allow a page fault to retry once.  We achieved
      this by clearing the FAULT_FLAG_ALLOW_RETRY flag when doing
      handle_mm_fault() the second time.  This was majorly used to avoid
      unexpected starvation of the system by looping over forever to handle the
      page fault on a single page.  However that should hardly happen, and after
      all for each code path to return a VM_FAULT_RETRY we'll first wait for a
      condition (during which time we should possibly yield the cpu) to happen
      before VM_FAULT_RETRY is really returned.
      
      This patch removes the restriction by keeping the FAULT_FLAG_ALLOW_RETRY
      flag when we receive VM_FAULT_RETRY.  It means that the page fault handler
      now can retry the page fault for multiple times if necessary without the
      need to generate another page fault event.  Meanwhile we still keep the
      FAULT_FLAG_TRIED flag so page fault handler can still identify whether a
      page fault is the first attempt or not.
      
      Then we'll have these combinations of fault flags (only considering
      ALLOW_RETRY flag and TRIED flag):
      
        - ALLOW_RETRY and !TRIED:  this means the page fault allows to
                                   retry, and this is the first try
      
        - ALLOW_RETRY and TRIED:   this means the page fault allows to
                                   retry, and this is not the first try
      
        - !ALLOW_RETRY and !TRIED: this means the page fault does not allow
                                   to retry at all
      
        - !ALLOW_RETRY and TRIED:  this is forbidden and should never be used
      
      In existing code we have multiple places that has taken special care of
      the first condition above by checking against (fault_flags &
      FAULT_FLAG_ALLOW_RETRY).  This patch introduces a simple helper to detect
      the first retry of a page fault by checking against both (fault_flags &
      FAULT_FLAG_ALLOW_RETRY) and !(fault_flag & FAULT_FLAG_TRIED) because now
      even the 2nd try will have the ALLOW_RETRY set, then use that helper in
      all existing special paths.  One example is in __lock_page_or_retry(), now
      we'll drop the mmap_sem only in the first attempt of page fault and we'll
      keep it in follow up retries, so old locking behavior will be retained.
      
      This will be a nice enhancement for current code [2] at the same time a
      supporting material for the future userfaultfd-writeprotect work, since in
      that work there will always be an explicit userfault writeprotect retry
      for protected pages, and if that cannot resolve the page fault (e.g., when
      userfaultfd-writeprotect is used in conjunction with swapped pages) then
      we'll possibly need a 3rd retry of the page fault.  It might also benefit
      other potential users who will have similar requirement like userfault
      write-protection.
      
      GUP code is not touched yet and will be covered in follow up patch.
      
      Please read the thread below for more information.
      
      [1] https://lore.kernel.org/lkml/20171102193644.GB22686@redhat.com/
      [2] https://lore.kernel.org/lkml/20181230154648.GB9832@redhat.com/
      
      
      
      Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Suggested-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Tested-by: default avatarBrian Geffon <bgeffon@google.com>
      Cc: Bobby Powers <bobbypowers@gmail.com>
      Cc: David Hildenbrand <david@redhat.com>
      Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
      Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Jerome Glisse <jglisse@redhat.com>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
      Cc: Martin Cracauer <cracauer@cons.org>
      Cc: Marty McFadden <mcfadden8@llnl.gov>
      Cc: Matthew Wilcox <willy@infradead.org>
      Cc: Maya Gokhale <gokhale2@llnl.gov>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Mike Kravetz <mike.kravetz@oracle.com>
      Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
      Cc: Pavel Emelyanov <xemul@openvz.org>
      Link: http://lkml.kernel.org/r/20200220160246.9790-1-peterx@redhat.com
      
      
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4064b982
  4. Apr 01, 2020
  5. Mar 31, 2020
  6. Mar 30, 2020
    • Mikel Rychliski's avatar
      PCI: Use ioremap(), not phys_to_virt() for platform ROM · 72e0ef0e
      Mikel Rychliski authored
      On some EFI systems, the video BIOS is provided by the EFI firmware.  The
      boot stub code stores the physical address of the ROM image in pdev->rom.
      Currently we attempt to access this pointer using phys_to_virt(), which
      doesn't work with CONFIG_HIGHMEM.
      
      On these systems, attempting to load the radeon module on a x86_32 kernel
      can result in the following:
      
        BUG: unable to handle page fault for address: 3e8ed03c
        #PF: supervisor read access in kernel mode
        #PF: error_code(0x0000) - not-present page
        *pde = 00000000
        Oops: 0000 [#1] PREEMPT SMP
        CPU: 0 PID: 317 Comm: systemd-udevd Not tainted 5.6.0-rc3-next-20200228 #2
        Hardware name: Apple Computer, Inc. MacPro1,1/Mac-F4208DC8, BIOS     MP11.88Z.005C.B08.0707021221 07/02/07
        EIP: radeon_get_bios+0x5ed/0xe50 [radeon]
        Code: 00 00 84 c0 0f 85 12 fd ff ff c7 87 64 01 00 00 00 00 00 00 8b 47 08 8b 55 b0 e8 1e 83 e1 d6 85 c0 74 1a 8b 55 c0 85 d2 74 13 <80> 38 55 75 0e 80 78 01 aa 0f 84 a4 03 00 00 8d 74 26 00 68 dc 06
        EAX: 3e8ed03c EBX: 00000000 ECX: 3e8ed03c EDX: 00010000
        ESI: 00040000 EDI: eec04000 EBP: eef3fc60 ESP: eef3fbe0
        DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010206
        CR0: 80050033 CR2: 3e8ed03c CR3: 2ec77000 CR4: 000006d0
        Call Trace:
         r520_init+0x26/0x240 [radeon]
         radeon_device_init+0x533/0xa50 [radeon]
         radeon_driver_load_kms+0x80/0x220 [radeon]
         drm_dev_register+0xa7/0x180 [drm]
         radeon_pci_probe+0x10f/0x1a0 [radeon]
         pci_device_probe+0xd4/0x140
      
      Fix the issue by updating all drivers which can access a platform provided
      ROM. Instead of calling the helper function pci_platform_rom() which uses
      phys_to_virt(), call ioremap() directly on the pdev->rom.
      
      radeon_read_platform_bios() previously directly accessed an __iomem
      pointer. Avoid this by calling memcpy_fromio() instead of kmemdup().
      
      pci_platform_rom() now has no remaining callers, so remove it.
      
      Link: https://lore.kernel.org/r/20200319021623.5426-1-mikel@mikelr.com
      
      
      Signed-off-by: default avatarMikel Rychliski <mikel@mikelr.com>
      Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
      Acked-by: default avatarAlex Deucher <alexander.deucher@amd.com>
      72e0ef0e
  7. Mar 27, 2020
  8. Mar 26, 2020
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