mm, compaction: Make sure we isolate a valid PFN
diff mbox series

Message ID 1558711908-15688-1-git-send-email-suzuki.poulose@arm.com
State Accepted
Commit e577c8b64d58fe307ea4d5149d31615df2d90861
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Series
  • mm, compaction: Make sure we isolate a valid PFN
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Commit Message

Suzuki K Poulose May 24, 2019, 3:31 p.m. UTC
When we have holes in a normal memory zone, we could endup having
cached_migrate_pfns which may not necessarily be valid, under heavy memory
pressure with swapping enabled ( via __reset_isolation_suitable(), triggered
by kswapd).

Later if we fail to find a page via fast_isolate_freepages(), we may
end up using the migrate_pfn we started the search with, as valid
page. This could lead to accessing NULL pointer derefernces like below,
due to an invalid mem_section pointer.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008 [47/1825]
 Mem abort info:
   ESR = 0x96000004
   Exception class = DABT (current EL), IL = 32 bits
   SET = 0, FnV = 0
   EA = 0, S1PTW = 0
 Data abort info:
   ISV = 0, ISS = 0x00000004
   CM = 0, WnR = 0
 user pgtable: 4k pages, 48-bit VAs, pgdp = 0000000082f94ae9
 [0000000000000008] pgd=0000000000000000
 Internal error: Oops: 96000004 [#1] SMP
 ...
 CPU: 10 PID: 6080 Comm: qemu-system-aar Not tainted 510-rc1+ #6
 Hardware name: AmpereComputing(R) OSPREY EV-883832-X3-0001/OSPREY, BIOS 4819 09/25/2018
 pstate: 60000005 (nZCv daif -PAN -UAO)
 pc : set_pfnblock_flags_mask+0x58/0xe8
 lr : compaction_alloc+0x300/0x950
 [...]
 Process qemu-system-aar (pid: 6080, stack limit = 0x0000000095070da5)
 Call trace:
  set_pfnblock_flags_mask+0x58/0xe8
  compaction_alloc+0x300/0x950
  migrate_pages+0x1a4/0xbb0
  compact_zone+0x750/0xde8
  compact_zone_order+0xd8/0x118
  try_to_compact_pages+0xb4/0x290
  __alloc_pages_direct_compact+0x84/0x1e0
  __alloc_pages_nodemask+0x5e0/0xe18
  alloc_pages_vma+0x1cc/0x210
  do_huge_pmd_anonymous_page+0x108/0x7c8
  __handle_mm_fault+0xdd4/0x1190
  handle_mm_fault+0x114/0x1c0
  __get_user_pages+0x198/0x3c0
  get_user_pages_unlocked+0xb4/0x1d8
  __gfn_to_pfn_memslot+0x12c/0x3b8
  gfn_to_pfn_prot+0x4c/0x60
  kvm_handle_guest_abort+0x4b0/0xcd8
  handle_exit+0x140/0x1b8
  kvm_arch_vcpu_ioctl_run+0x260/0x768
  kvm_vcpu_ioctl+0x490/0x898
  do_vfs_ioctl+0xc4/0x898
  ksys_ioctl+0x8c/0xa0
  __arm64_sys_ioctl+0x28/0x38
  el0_svc_common+0x74/0x118
  el0_svc_handler+0x38/0x78
  el0_svc+0x8/0xc
 Code: f8607840 f100001f 8b011401 9a801020 (f9400400)
 ---[ end trace af6a35219325a9b6 ]---

The issue was reported on an arm64 server with 128GB with holes in the zone
(e.g, [32GB@4GB, 96GB@544GB]), with a swap device enabled, while running 100 KVM
guest instances.

This patch fixes the issue by ensuring that the page belongs to a valid PFN
when we fallback to using the lower limit of the scan range upon failure in
fast_isolate_freepages().

Fixes: 5a811889de10f1eb ("mm, compaction: use free lists to quickly locate a migration target")
Reported-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Mel Gorman May 24, 2019, 3:51 p.m. UTC | #1
On Fri, May 24, 2019 at 04:31:48PM +0100, Suzuki K Poulose wrote:
> When we have holes in a normal memory zone, we could endup having
> cached_migrate_pfns which may not necessarily be valid, under heavy memory
> pressure with swapping enabled ( via __reset_isolation_suitable(), triggered
> by kswapd).
> 
> Later if we fail to find a page via fast_isolate_freepages(), we may
> end up using the migrate_pfn we started the search with, as valid
> page. This could lead to accessing NULL pointer derefernces like below,
> due to an invalid mem_section pointer.
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008 [47/1825]
>  Mem abort info:
>    ESR = 0x96000004
>    Exception class = DABT (current EL), IL = 32 bits
>    SET = 0, FnV = 0
>    EA = 0, S1PTW = 0
>  Data abort info:
>    ISV = 0, ISS = 0x00000004
>    CM = 0, WnR = 0
>  user pgtable: 4k pages, 48-bit VAs, pgdp = 0000000082f94ae9
>  [0000000000000008] pgd=0000000000000000
>  Internal error: Oops: 96000004 [#1] SMP
>  ...
>  CPU: 10 PID: 6080 Comm: qemu-system-aar Not tainted 510-rc1+ #6
>  Hardware name: AmpereComputing(R) OSPREY EV-883832-X3-0001/OSPREY, BIOS 4819 09/25/2018
>  pstate: 60000005 (nZCv daif -PAN -UAO)
>  pc : set_pfnblock_flags_mask+0x58/0xe8
>  lr : compaction_alloc+0x300/0x950
>  [...]
>  Process qemu-system-aar (pid: 6080, stack limit = 0x0000000095070da5)
>  Call trace:
>   set_pfnblock_flags_mask+0x58/0xe8
>   compaction_alloc+0x300/0x950
>   migrate_pages+0x1a4/0xbb0
>   compact_zone+0x750/0xde8
>   compact_zone_order+0xd8/0x118
>   try_to_compact_pages+0xb4/0x290
>   __alloc_pages_direct_compact+0x84/0x1e0
>   __alloc_pages_nodemask+0x5e0/0xe18
>   alloc_pages_vma+0x1cc/0x210
>   do_huge_pmd_anonymous_page+0x108/0x7c8
>   __handle_mm_fault+0xdd4/0x1190
>   handle_mm_fault+0x114/0x1c0
>   __get_user_pages+0x198/0x3c0
>   get_user_pages_unlocked+0xb4/0x1d8
>   __gfn_to_pfn_memslot+0x12c/0x3b8
>   gfn_to_pfn_prot+0x4c/0x60
>   kvm_handle_guest_abort+0x4b0/0xcd8
>   handle_exit+0x140/0x1b8
>   kvm_arch_vcpu_ioctl_run+0x260/0x768
>   kvm_vcpu_ioctl+0x490/0x898
>   do_vfs_ioctl+0xc4/0x898
>   ksys_ioctl+0x8c/0xa0
>   __arm64_sys_ioctl+0x28/0x38
>   el0_svc_common+0x74/0x118
>   el0_svc_handler+0x38/0x78
>   el0_svc+0x8/0xc
>  Code: f8607840 f100001f 8b011401 9a801020 (f9400400)
>  ---[ end trace af6a35219325a9b6 ]---
> 
> The issue was reported on an arm64 server with 128GB with holes in the zone
> (e.g, [32GB@4GB, 96GB@544GB]), with a swap device enabled, while running 100 KVM
> guest instances.
> 
> This patch fixes the issue by ensuring that the page belongs to a valid PFN
> when we fallback to using the lower limit of the scan range upon failure in
> fast_isolate_freepages().
> 
> Fixes: 5a811889de10f1eb ("mm, compaction: use free lists to quickly locate a migration target")
> Reported-by: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Mel Gorman <mgorman@techsingularity.net>
Anshuman Khandual May 27, 2019, 5:38 a.m. UTC | #2
On 05/24/2019 09:01 PM, Suzuki K Poulose wrote:
> When we have holes in a normal memory zone, we could endup having
> cached_migrate_pfns which may not necessarily be valid, under heavy memory
> pressure with swapping enabled ( via __reset_isolation_suitable(), triggered
> by kswapd).
> 
> Later if we fail to find a page via fast_isolate_freepages(), we may
> end up using the migrate_pfn we started the search with, as valid
> page. This could lead to accessing NULL pointer derefernces like below,
> due to an invalid mem_section pointer.
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008 [47/1825]
>  Mem abort info:
>    ESR = 0x96000004
>    Exception class = DABT (current EL), IL = 32 bits
>    SET = 0, FnV = 0
>    EA = 0, S1PTW = 0
>  Data abort info:
>    ISV = 0, ISS = 0x00000004
>    CM = 0, WnR = 0
>  user pgtable: 4k pages, 48-bit VAs, pgdp = 0000000082f94ae9
>  [0000000000000008] pgd=0000000000000000
>  Internal error: Oops: 96000004 [#1] SMP
>  ...
>  CPU: 10 PID: 6080 Comm: qemu-system-aar Not tainted 510-rc1+ #6
>  Hardware name: AmpereComputing(R) OSPREY EV-883832-X3-0001/OSPREY, BIOS 4819 09/25/2018
>  pstate: 60000005 (nZCv daif -PAN -UAO)
>  pc : set_pfnblock_flags_mask+0x58/0xe8
>  lr : compaction_alloc+0x300/0x950
>  [...]
>  Process qemu-system-aar (pid: 6080, stack limit = 0x0000000095070da5)
>  Call trace:
>   set_pfnblock_flags_mask+0x58/0xe8
>   compaction_alloc+0x300/0x950
>   migrate_pages+0x1a4/0xbb0
>   compact_zone+0x750/0xde8
>   compact_zone_order+0xd8/0x118
>   try_to_compact_pages+0xb4/0x290
>   __alloc_pages_direct_compact+0x84/0x1e0
>   __alloc_pages_nodemask+0x5e0/0xe18
>   alloc_pages_vma+0x1cc/0x210
>   do_huge_pmd_anonymous_page+0x108/0x7c8
>   __handle_mm_fault+0xdd4/0x1190
>   handle_mm_fault+0x114/0x1c0
>   __get_user_pages+0x198/0x3c0
>   get_user_pages_unlocked+0xb4/0x1d8
>   __gfn_to_pfn_memslot+0x12c/0x3b8
>   gfn_to_pfn_prot+0x4c/0x60
>   kvm_handle_guest_abort+0x4b0/0xcd8
>   handle_exit+0x140/0x1b8
>   kvm_arch_vcpu_ioctl_run+0x260/0x768
>   kvm_vcpu_ioctl+0x490/0x898
>   do_vfs_ioctl+0xc4/0x898
>   ksys_ioctl+0x8c/0xa0
>   __arm64_sys_ioctl+0x28/0x38
>   el0_svc_common+0x74/0x118
>   el0_svc_handler+0x38/0x78
>   el0_svc+0x8/0xc
>  Code: f8607840 f100001f 8b011401 9a801020 (f9400400)
>  ---[ end trace af6a35219325a9b6 ]---
> 
> The issue was reported on an arm64 server with 128GB with holes in the zone
> (e.g, [32GB@4GB, 96GB@544GB]), with a swap device enabled, while running 100 KVM
> guest instances.
> 
> This patch fixes the issue by ensuring that the page belongs to a valid PFN
> when we fallback to using the lower limit of the scan range upon failure in
> fast_isolate_freepages().
> 
> Fixes: 5a811889de10f1eb ("mm, compaction: use free lists to quickly locate a migration target")
> Reported-by: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

Patch
diff mbox series

diff --git a/mm/compaction.c b/mm/compaction.c
index 9febc8c..9e1b9ac 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1399,7 +1399,7 @@  fast_isolate_freepages(struct compact_control *cc)
 				page = pfn_to_page(highest);
 				cc->free_pfn = highest;
 			} else {
-				if (cc->direct_compaction) {
+				if (cc->direct_compaction && pfn_valid(min_pfn)) {
 					page = pfn_to_page(min_pfn);
 					cc->free_pfn = min_pfn;
 				}