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FAILED: patch "[PATCH] mm/page_alloc.c: fix uninitialized memmaps on a partially" failed to apply to 4.19-stable tree

PATCH [email protected] 2 participants 2 messages Feb 9, 2020

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The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e822969cab48b786b64246aad1a3ba2a774f5d23 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <[email protected]>
Date: Mon, 3 Feb 2020 17:33:48 -0800
Subject: [PATCH] mm/page_alloc.c: fix uninitialized memmaps on a partially
populated last section

Patch series "mm: fix max_pfn not falling on section boundary", v2.

Playing with different memory sizes for a x86-64 guest, I discovered that some memmaps (highest section if max_mem does not fall on the section boundary) are marked as being valid and online, but contain garbage. We have to properly initialize these memmaps.

Looking at /proc/kpageflags and friends, I found some more issues, partially related to this.

This patch (of 3):

If max_pfn is not aligned to a section boundary, we can easily run into BUGs. This can e.g., be triggered on x86-64 under QEMU by specifying a memory size that is not a multiple of 128MB (e.g., 4097MB, but also 4160MB). I was told that on real HW, we can easily have this scenario (esp., one of the main reasons sub-section hotadd of devmem was added).

The issue is, that we have a valid memmap (pfn_valid()) for the whole section, and the whole section will be marked "online". pfn_to_online_page() will succeed, but the memmap contains garbage.

E.g., doing a "./page-types -r -a 0x144001" when QEMU was started with "-m 4160M" - (see tools/vm/page-types.c):

[  200.476376] BUG: unable to handle page fault for address: fffffffffffffffe
[  200.477500] #PF: supervisor read access in kernel mode
[  200.478334] #PF: error_code(0x0000) - not-present page
[  200.479076] PGD 59614067 P4D 59614067 PUD 59616067 PMD 0
[  200.479557] Oops: 0000 [#4] SMP NOPTI
[  200.479875] CPU: 0 PID: 603 Comm: page-types Tainted: G      D W         5.5.0-rc1-next-20191209 #93
[  200.480646] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu4
[  200.481648] RIP: 0010:stable_page_flags+0x4d/0x410
[  200.482061] Code: f3 ff 41 89 c0 48 b8 00 00 00 00 01 00 00 00 45 84 c0 0f 85 cd 02 00 00 48 8b 53 08 48 8b 2b 48f
[  200.483644] RSP: 0018:ffffb139401cbe60 EFLAGS: 00010202
[  200.484091] RAX: fffffffffffffffe RBX: fffffbeec5100040 RCX: 0000000000000000
[  200.484697] RDX: 0000000000000001 RSI: ffffffff9535c7cd RDI: 0000000000000246
[  200.485313] RBP: ffffffffffffffff R08: 0000000000000000 R09: 0000000000000000
[  200.485917] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000144001
[  200.486523] R13: 00007ffd6ba55f48 R14: 00007ffd6ba55f40 R15: ffffb139401cbf08
[  200.487130] FS:  00007f68df717580(0000) GS:ffff9ec77fa00000(0000) knlGS:0000000000000000
[  200.487804] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  200.488295] CR2: fffffffffffffffe CR3: 0000000135d48000 CR4: 00000000000006f0
[  200.488897] Call Trace:
[  200.489115]  kpageflags_read+0xe9/0x140
[  200.489447]  proc_reg_read+0x3c/0x60
[  200.489755]  vfs_read+0xc2/0x170
[  200.490037]  ksys_pread64+0x65/0xa0
[  200.490352]  do_syscall_64+0x5c/0xa0
[  200.490665]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

But it can be triggered much easier via "cat /proc/kpageflags > /dev/null" after cold/hot plugging a DIMM to such a system:

[root@localhost ~]# cat /proc/kpageflags > /dev/null

[  111.517275] BUG: unable to handle page fault for address: fffffffffffffffe
[  111.517907] #PF: supervisor read access in kernel mode
[  111.518333] #PF: error_code(0x0000) - not-present page
[  111.518771] PGD a240e067 P4D a240e067 PUD a2410067 PMD 0

This patch fixes that by at least zero-ing out that memmap (so e.g., page_to_pfn() will not crash). Commit 907ec5fca3dc ("mm: zero remaining unavailable struct pages") tried to fix a similar issue, but forgot to consider this special case.

After this patch, there are still problems to solve. E.g., not all of these pages falling into a memory hole will actually get initialized later and set PageReserved - they are only zeroed out - but at least the immediate crashes are gone. A follow-up patch will take care of this.

Link http://lkml.kernel.org/r/[email protected] open here
Fixes f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
Signed-off-by David Hildenbrand <[email protected]>
Tested-by Daniel Jordan <[email protected]>
Cc Naoya Horiguchi <[email protected]>
Cc Pavel Tatashin <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Steven Sistare <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Daniel Jordan <[email protected]>
Cc Bob Picco <[email protected]>
Cc Oscar Salvador <[email protected]>
Cc Alexey Dobriyan <[email protected]>
Cc Dan Williams <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Stephen Rothwell <[email protected]>
Cc <[email protected]> [4.15+]
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
mm/page_alloc.c +12 -2
index 15e908ad933b..10eeaaadf53a 100644
@@ -6947,7 +6947,8 @@ static u64 zero_pfn_range(unsigned long spfn, unsigned long epfn)
  * This function also addresses a similar issue where struct pages are left
  * uninitialized because the physical address range is not covered by
  * memblock.memory or memblock.reserved. That could happen when memblock
- * layout is manually configured via memmap=.
+ * layout is manually configured via memmap=, or when the highest physical
+ * address (max_pfn) does not end on a section boundary.
  */
 void __init zero_resv_unavail(void)
 {

@@ -6965,7 +6966,16 @@ void __init zero_resv_unavail(void)
 			pgcnt += zero_pfn_range(PFN_DOWN(next), PFN_UP(start));
 		next = end;
 	}
-	pgcnt += zero_pfn_range(PFN_DOWN(next), max_pfn);
+
+	/*
+	 * Early sections always have a fully populated memmap for the whole
+	 * section - see pfn_valid(). If the last section has holes at the
+	 * end and that section is marked "online", the memmap will be
+	 * considered initialized. Make sure that memmap has a well defined
+	 * state.
+	 */
+	pgcnt += zero_pfn_range(PFN_DOWN(next),
+				round_up(max_pfn, PAGES_PER_SECTION));
 
 	/*
 	 * Struct pages that do not have backing memory. This could be because
maintainer
#1 lore raw
Quoted 99 lines · On Sun, Feb 09, 2020 at 01:40:23PM +0100, [email protected] wrote:

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e822969cab48b786b64246aad1a3ba2a774f5d23 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <[email protected]>
Date: Mon, 3 Feb 2020 17:33:48 -0800
Subject: [PATCH] mm/page_alloc.c: fix uninitialized memmaps on a partially populated last section

Patch series "mm: fix max_pfn not falling on section boundary", v2.

Playing with different memory sizes for a x86-64 guest, I discovered that some memmaps (highest section if max_mem does not fall on the section boundary) are marked as being valid and online, but contain garbage. We have to properly initialize these memmaps.

Looking at /proc/kpageflags and friends, I found some more issues, partially related to this.

This patch (of 3):

If max_pfn is not aligned to a section boundary, we can easily run into BUGs. This can e.g., be triggered on x86-64 under QEMU by specifying a memory size that is not a multiple of 128MB (e.g., 4097MB, but also 4160MB). I was told that on real HW, we can easily have this scenario (esp., one of the main reasons sub-section hotadd of devmem was added).

The issue is, that we have a valid memmap (pfn_valid()) for the whole section, and the whole section will be marked "online". pfn_to_online_page() will succeed, but the memmap contains garbage.

E.g., doing a "./page-types -r -a 0x144001" when QEMU was started with "-m 4160M" - (see tools/vm/page-types.c):

[  200.476376] BUG: unable to handle page fault for address: fffffffffffffffe
[  200.477500] #PF: supervisor read access in kernel mode
[  200.478334] #PF: error_code(0x0000) - not-present page
[  200.479076] PGD 59614067 P4D 59614067 PUD 59616067 PMD 0
[  200.479557] Oops: 0000 [#4] SMP NOPTI
[  200.479875] CPU: 0 PID: 603 Comm: page-types Tainted: G      D W         5.5.0-rc1-next-20191209 #93
[  200.480646] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu4
[  200.481648] RIP: 0010:stable_page_flags+0x4d/0x410
[  200.482061] Code: f3 ff 41 89 c0 48 b8 00 00 00 00 01 00 00 00 45 84 c0 0f 85 cd 02 00 00 48 8b 53 08 48 8b 2b 48f
[  200.483644] RSP: 0018:ffffb139401cbe60 EFLAGS: 00010202
[  200.484091] RAX: fffffffffffffffe RBX: fffffbeec5100040 RCX: 0000000000000000
[  200.484697] RDX: 0000000000000001 RSI: ffffffff9535c7cd RDI: 0000000000000246
[  200.485313] RBP: ffffffffffffffff R08: 0000000000000000 R09: 0000000000000000
[  200.485917] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000144001
[  200.486523] R13: 00007ffd6ba55f48 R14: 00007ffd6ba55f40 R15: ffffb139401cbf08
[  200.487130] FS:  00007f68df717580(0000) GS:ffff9ec77fa00000(0000) knlGS:0000000000000000
[  200.487804] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  200.488295] CR2: fffffffffffffffe CR3: 0000000135d48000 CR4: 00000000000006f0
[  200.488897] Call Trace:
[  200.489115]  kpageflags_read+0xe9/0x140
[  200.489447]  proc_reg_read+0x3c/0x60
[  200.489755]  vfs_read+0xc2/0x170
[  200.490037]  ksys_pread64+0x65/0xa0
[  200.490352]  do_syscall_64+0x5c/0xa0
[  200.490665]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

But it can be triggered much easier via "cat /proc/kpageflags > /dev/null" after cold/hot plugging a DIMM to such a system:

[root@localhost ~]# cat /proc/kpageflags > /dev/null

[  111.517275] BUG: unable to handle page fault for address: fffffffffffffffe
[  111.517907] #PF: supervisor read access in kernel mode
[  111.518333] #PF: error_code(0x0000) - not-present page
[  111.518771] PGD a240e067 P4D a240e067 PUD a2410067 PMD 0

This patch fixes that by at least zero-ing out that memmap (so e.g., page_to_pfn() will not crash). Commit 907ec5fca3dc ("mm: zero remaining unavailable struct pages") tried to fix a similar issue, but forgot to consider this special case.

After this patch, there are still problems to solve. E.g., not all of these pages falling into a memory hole will actually get initialized later and set PageReserved - they are only zeroed out - but at least the immediate crashes are gone. A follow-up patch will take care of this.

Link http://lkml.kernel.org/r/[email protected] open here
Fixes f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
Signed-off-by David Hildenbrand <[email protected]>
Tested-by Daniel Jordan <[email protected]>
Cc Naoya Horiguchi <[email protected]>
Cc Pavel Tatashin <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Steven Sistare <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Daniel Jordan <[email protected]>
Cc Bob Picco <[email protected]>
Quoted 8 lines
Cc Oscar Salvador <[email protected]>
Cc Alexey Dobriyan <[email protected]>
Cc Dan Williams <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Stephen Rothwell <[email protected]>
Cc <[email protected]> [4.15+]
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>

I took these two additional patches for 4.19:

ec393a0f014e ("mm: return zero_resv_unavail optimization") 907ec5fca3dc ("mm: zero remaining unavailable struct pages")

Signature · 2 lines
Thanks,
Sasha