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Date:   Thu, 27 May 2021 19:22:00 +0300
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Qian Cai <quic_qiancai@quicinc.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Arm64 crash while reading memory sysfs
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On Thu, May 27, 2021 at 10:33:13AM -0400, Qian Cai wrote:
> 
> 
> On 5/27/2021 4:56 AM, Mike Rapoport wrote:
> > Let's drop memblock=debug for now and add this instead:
> 
> [    0.000000][    T0] Booting Linux on physical CPU 0x0000000000 [0x503f0002]
> [    0.000000][    T0] Linux version 5.13.0-rc3-next-20210526+ (root@admin5) (gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #31 SMP Thu May 27 12:32:40 UTC 2021
> [    0.000000][    T0] Inode-cache hash table entries: 4194304 (order: 9, 33554432 bytes, linear)
> [    0.000000][    T0] mem auto-init: stack:off, heap alloc:on, heap free:off
> [    0.000000][    T0] MEMBLOCK configuration:
> [    0.000000][    T0]  memory size = 0x0000001ff0000000 reserved size = 0x0000000421e33ae8
> [    0.000000][    T0]  memory.cnt  = 0xc
> [    0.000000][    T0] Memory: 777216K/133955584K available (17984K kernel code, 118722K rwdata, 4416K rodata, 6080K init, 67276K bss, 17379072K reserved, 0K cma-reserved)

I still cannot understand where most of the memory disappeared, but it
seems entirely different issue.
 
> > Sorry, I've missed that the BUG is apparently triggered for pfn + i. Can
> > you please try this instead:
> 
> [  259.216661][ T1417] test_pages_in_a_zone: pfn 8000 is not valid
> [  259.226547][ T1417] page:00000000f4aa8c5c is uninitialized and poisoned
> [  259.226560][ T1417] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))

Can you please try Anshuman's patch "arm64/mm: Drop HAVE_ARCH_PFN_VALID":

https://lore.kernel.org/lkml/1621947349-25421-1-git-send-email-anshuman.khandual@arm.com

It seems to me that the check for memblock_is_memory() in
arm64::pfn_valid() is what makes init_unavailable_range() to bail out for
section parts that are not actually populated and then we have
VM_BUG_ON_PAGE(PagePoisoned(p)) for these pages.

-- 
Sincerely yours,
Mike.