On Fri 15-06-18 07:29:48, Naoya Horiguchi wrote:
[...]
> From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Date: Thu, 14 Jun 2018 16:04:36 +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>
> Tested-by: Oscar Salvador <osalvador@xxxxxxx>
OK, this makes sense to me. It is definitely much better than the
original attempt.
Unless I am missing something this should be correct
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> arch/x86/kernel/e820.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index d1f25c831447..c88c23c658c1 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 addr = 0;
>
> /*
> * The bootstrap memblock region count maximum is 128 entries
> @@ -1264,13 +1265,21 @@ void __init e820__memblock_setup(void)
> struct e820_entry *entry = &e820_table->entries[i];
>
> end = entry->addr + entry->size;
> + if (addr < entry->addr)
> + memblock_reserve(addr, entry->addr - addr);
> + addr = end;
> if (end != (resource_size_t)end)
> continue;
>
> + /*
> + * all !E820_TYPE_RAM ranges (including gap ranges) 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 && entry->type != E820_TYPE_RESERVED_KERN)
> - continue;
> -
> - memblock_add(entry->addr, entry->size);
> + memblock_reserve(entry->addr, entry->size);
> + else
> + memblock_add(entry->addr, entry->size);
> }
>
> /* Throw away partial pages: */
> --
> 2.7.4
--
Michal Hocko
SUSE Labs
