[PATCH v2] x86/e820: put !E820_TYPE_RAM regions into memblock.reserved
From: Naoya Horiguchi
Date: Thu Jun 14 2018 - 02:38:42 EST
On Thu, Jun 14, 2018 at 07:38:59AM +0200, Oscar Salvador wrote:
> On Thu, Jun 14, 2018 at 05:16:18AM +0000, Naoya Horiguchi wrote:
...
> >
> > My concern is that there are a few E820 memory types rather than
> > E820_TYPE_RAM and E820_TYPE_RESERVED, and I'm not sure that putting them
> > all into memblock.reserved is really acceptable.
>
> Hi Naoya,
>
> Maybe you could just add to memblock.reserved, all unavailable ranges within
> E820_TYPE_RAM.
> Actually, in your original patch, you are walking memblock.memory, which should
> only contain E820_TYPE_RAM ranges (talking about x86).
>
> So I think the below would to the trick as well?
>
> @@ -1248,6 +1276,7 @@ void __init e820__memblock_setup(void)
> {
> int i;
> u64 end;
> + u64 next = 0;
>
> /*
> * The bootstrap memblock region count maximum is 128 entries
>
> @@ -1269,6 +1299,14 @@ void __init e820__memblock_setup(void)
>
> if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN)
> continue;
>
> +
> + if (entry->type == E820_TYPE_RAM)
> + if (next < entry->addr) {
> + memblock_reserve (next, next + (entry->addr - next));
> + next = end;
> + }
>
> With the above patch, I can no longer see the issues either.
I double-checked and this change looks good to me.
>
> Although, there is a difference between this and your original patch.
> In your original patch, you are just zeroing the pages, while with this one (or with your second patch),
> we will zero the page in reserve_bootmem_region(), but that function also init
> some other fields of the struct page:
>
> mm_zero_struct_page(page);
> set_page_links(page, zone, nid, pfn);
> init_page_count(page);
> page_mapcount_reset(page);
> page_cpupid_reset_last(page);
>
> So I am not sure we want to bother doing that for pages that are really unreachable.
I think that considering that /proc/kpageflags can check them, some data
(even if it's trivial) might be better than just zeros.
Here's the updated patch.
Thanks for the suggestion and testing!
---
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Date: Thu, 14 Jun 2018 14:44:36 +0900
Subject: [PATCH] x86/e820: put !E820_TYPE_RAM regions into memblock.reserved
There is a kernel panic that is triggered when reading /proc/kpageflags
on the kernel booted with kernel parameter 'memmap=nn[KMG]!ss[KMG]':
BUG: unable to handle kernel paging request at fffffffffffffffe
PGD 9b20e067 P4D 9b20e067 PUD 9b210067 PMD 0
Oops: 0000 [#1] SMP PTI
CPU: 2 PID: 1728 Comm: page-types Not tainted 4.17.0-rc6-mm1-v4.17-rc6-180605-0816-00236-g2dfb086ef02c+ #160
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.fc28 04/01/2014
RIP: 0010:stable_page_flags+0x27/0x3c0
Code: 00 00 00 0f 1f 44 00 00 48 85 ff 0f 84 a0 03 00 00 41 54 55 49 89 fc 53 48 8b 57 08 48 8b 2f 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 01 0f 84 10 03 00 00 31 db 49 8b 54 24 08 4c 89 e7
RSP: 0018:ffffbbd44111fde0 EFLAGS: 00010202
RAX: fffffffffffffffe RBX: 00007fffffffeff9 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000202 RDI: ffffed1182fff5c0
RBP: ffffffffffffffff R08: 0000000000000001 R09: 0000000000000001
R10: ffffbbd44111fed8 R11: 0000000000000000 R12: ffffed1182fff5c0
R13: 00000000000bffd7 R14: 0000000002fff5c0 R15: ffffbbd44111ff10
FS: 00007efc4335a500(0000) GS:ffff93a5bfc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffffe CR3: 00000000b2a58000 CR4: 00000000001406e0
Call Trace:
kpageflags_read+0xc7/0x120
proc_reg_read+0x3c/0x60
__vfs_read+0x36/0x170
vfs_read+0x89/0x130
ksys_pread64+0x71/0x90
do_syscall_64+0x5b/0x160
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7efc42e75e23
Code: 09 00 ba 9f 01 00 00 e8 ab 81 f4 ff 66 2e 0f 1f 84 00 00 00 00 00 90 83 3d 29 0a 2d 00 00 75 13 49 89 ca b8 11 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 34 c3 48 83 ec 08 e8 db d3 01 00 48 89 04 24
According to kernel bisection, this problem became visible due to commit
f7f99100d8d9 which changes how struct pages are initialized.
Memblock layout affects the pfn ranges covered by node/zone. Consider
that we have a VM with 2 NUMA nodes and each node has 4GB memory, and
the default (no memmap= given) memblock layout is like below:
MEMBLOCK configuration:
memory size = 0x00000001fff75c00 reserved size = 0x000000000300c000
memory.cnt = 0x4
memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0
memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0
memory[0x2] [0x0000000100000000-0x000000013fffffff], 0x0000000040000000 bytes on node 0 flags: 0x0
memory[0x3] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0
...
If you give memmap=1G!4G (so it just covers memory[0x2]),
the range [0x100000000-0x13fffffff] is gone:
MEMBLOCK configuration:
memory size = 0x00000001bff75c00 reserved size = 0x000000000300c000
memory.cnt = 0x3
memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0
memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0
memory[0x2] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0
...
This causes shrinking node 0's pfn range because it is calculated by
the address range of memblock.memory. So some of struct pages in the
gap range are left uninitialized.
We have a function zero_resv_unavail() which does zeroing the struct
pages within the reserved unavailable range (i.e. memblock.memory &&
!memblock.reserved). This patch utilizes it to cover all unavailable
ranges by putting them into memblock.reserved.
Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Suggested-by: Oscar Salvador <osalvador@xxxxxxxxxxxxxxxxxx>
Tested-by: Oscar Salvador <osalvador@xxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/e820.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index d1f25c831447..d15ef47ea354 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1248,6 +1248,7 @@ void __init e820__memblock_setup(void)
{
int i;
u64 end;
+ u64 next = 0;
/*
* The bootstrap memblock region count maximum is 128 entries
@@ -1270,6 +1271,17 @@ void __init e820__memblock_setup(void)
if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN)
continue;
+ /*
+ * Ranges unavailable in E820_TYPE_RAM are put into
+ * memblock.reserved, to make sure that struct pages in such
+ * regions are not left uninitialized after bootup.
+ */
+ if (entry->type == E820_TYPE_RAM)
+ if (next < entry->addr) {
+ memblock_reserve (next, next + (entry->addr - next));
+ next = end;
+ }
+
memblock_add(entry->addr, entry->size);
}
--
2.7.4