Re: [PATCH v2] x86/e820: put !E820_TYPE_RAM regions into memblock.reserved

[Oscar Salvador]

On Thu, Jun 14, 2018 at 06:34:55AM +0000, Naoya Horiguchi wrote:
> 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);
>  	}

Thanks Naoya!

Andrew: In case you consider to take this patch instead of the first one,
could you please replace "osalvador@xxxxxxxxxxxxxxxxxx" with "osalvador@xxxxxxx"?

Thanks

Best Regards
Oscar Salvador