linux-kernel - Re: [PATCH 1/4] mm/page_alloc: always initialize memory map for the holes

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Date:   Sat, 31 Jul 2021 12:11:16 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Simek <monstr@...str.eu>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/4] mm/page_alloc: always initialize memory map for the
 holes

Hi,

On 7/31/21 11:30 AM, Mike Rapoport wrote:
> On Sat, Jul 31, 2021 at 09:56:01AM -0700, Guenter Roeck wrote:
>> Hi,
>>
>> On Wed, Jul 14, 2021 at 03:37:36PM +0300, Mike Rapoport wrote:
>>> From: Mike Rapoport <rppt@...ux.ibm.com>
>>>
>>> Currently memory map for the holes is initialized only when SPARSEMEM
>>> memory model is used. Yet, even with FLATMEM there could be holes in the
>>> physical memory layout that have memory map entries.
>>>
>>> For instance, the memory reserved using e820 API on i386 or
>>> "reserved-memory" nodes in device tree would not appear in memblock.memory
>>> and hence the struct pages for such holes will be skipped during memory map
>>> initialization.
>>>
>>> These struct pages will be zeroed because the memory map for FLATMEM
>>> systems is allocated with memblock_alloc_node() that clears the allocated
>>> memory. While zeroed struct pages do not cause immediate problems, the
>>> correct behaviour is to initialize every page using __init_single_page().
>>> Besides, enabling page poison for FLATMEM case will trigger
>>> PF_POISONED_CHECK() unless the memory map is properly initialized.
>>>
>>> Make sure init_unavailable_range() is called for both SPARSEMEM and FLATMEM
>>> so that struct pages representing memory holes would appear as PG_Reserved
>>> with any memory layout.
>>>
>>> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
>>
>> This patch causes microblaze petalogix-ml605 qemu emulations to fail
>> silently (no console output). Reverting it fixes the problem.
> 
> It appears that petalogix-ml605 memory starts at 0x50000, but microblaze's
> pfn_valid does not reject pfns < ARCH_PFN_OFFSET.
> 
> This should fix the issue:
> 
> diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h
> index ce550978f4fc..4b8b2fa78fc5 100644
> --- a/arch/microblaze/include/asm/page.h
> +++ b/arch/microblaze/include/asm/page.h
> @@ -112,8 +112,7 @@ extern int page_is_ram(unsigned long pfn);
>   #  define page_to_phys(page)     (page_to_pfn(page) << PAGE_SHIFT)
>   
>   #  define ARCH_PFN_OFFSET	(memory_start >> PAGE_SHIFT)
> -#  define pfn_valid(pfn)	((pfn) < (max_mapnr + ARCH_PFN_OFFSET))
> -
> +#  define pfn_valid(pfn)	((pfn) >= ARCH_PFN_OFFSET && (pfn) < (max_mapnr + ARCH_PFN_OFFSET))
>   # endif /* __ASSEMBLY__ */
>   
>   #define	virt_addr_valid(vaddr)	(pfn_valid(virt_to_pfn(vaddr)))

Indeed, that does the trick.

Feel free to add

Tested-by: Guenter Roeck <linux@...ck-us.net>

to the patch.

Thanks,
Guenter

>> Guenter
>>
>> ---
>> Bisect log:
>>
>> # bad: [8d4b477da1a807199ca60e0829357ce7aa6758d5] Add linux-next specific files for 20210730
>> # good: [ff1176468d368232b684f75e82563369208bc371] Linux 5.14-rc3
>> git bisect start 'HEAD' 'v5.14-rc3'
>> # good: [8f3eb1f5c702ef868d89799b03c21d122f2fe197] Merge remote-tracking branch 'bpf-next/for-next'
>> git bisect good 8f3eb1f5c702ef868d89799b03c21d122f2fe197
>> # good: [32286c7080c56c835f25302c38eebccf41b7b576] Merge remote-tracking branch 'tip/auto-latest'
>> git bisect good 32286c7080c56c835f25302c38eebccf41b7b576
>> # good: [70c40604c7d393f95171f49717a27bf8e05b5439] Merge remote-tracking branch 'dmaengine/next'
>> git bisect good 70c40604c7d393f95171f49717a27bf8e05b5439
>> # good: [b038834891b35ec410693028a500f769db132a81] Merge remote-tracking branch 'rust/rust-next'
>> git bisect good b038834891b35ec410693028a500f769db132a81
>> # bad: [d8f4e506a9ba375110945d75573b3304491e6350] memory-hotplug.rst: complete admin-guide overhaul
>> git bisect bad d8f4e506a9ba375110945d75573b3304491e6350
>> # good: [bef692dcfb7cdb5c960abfc31e2386a0ff41af54] lazy tlb: shoot lazies, a non-refcounting lazy tlb option
>> git bisect good bef692dcfb7cdb5c960abfc31e2386a0ff41af54
>> # bad: [5fcd957e2f0dc4cb25a6ee60ebfb1200de09c9d1] mm-migrate-demote-pages-during-reclaim-v11
>> git bisect bad 5fcd957e2f0dc4cb25a6ee60ebfb1200de09c9d1
>> # good: [8c2a82ab20eb09d217446989ae209f5ff19a64ac] mm/vmalloc: use batched page requests in bulk-allocator
>> git bisect good 8c2a82ab20eb09d217446989ae209f5ff19a64ac
>> # bad: [c36a5446e29f1461780b06785769b9402522f847] mm/page_alloc.c: fix 'zone_id' may be used uninitialized in this function warning
>> git bisect bad c36a5446e29f1461780b06785769b9402522f847
>> # good: [05e358c552628e26be3985933bea88e7512414c0] mm/kasan: move kasan.fault to mm/kasan/report.c
>> git bisect good 05e358c552628e26be3985933bea88e7512414c0
>> # bad: [b467ff7f560908e60ca181658b7ee48e5da94da1] microblaze: simplify pte_alloc_one_kernel()
>> git bisect bad b467ff7f560908e60ca181658b7ee48e5da94da1
>> # bad: [d2a572bf593a57246827bd79c91fe2ee6b7af1f0] mm/page_alloc: always initialize memory map for the holes
>> git bisect bad d2a572bf593a57246827bd79c91fe2ee6b7af1f0
>> # first bad commit: [d2a572bf593a57246827bd79c91fe2ee6b7af1f0] mm/page_alloc: always initialize memory map for the holes
>