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From: Mike Rapoport <rppt@linux.ibm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Qian Cai (QUIC)" <quic_qiancai@quicinc.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.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
Date: Wed, 26 May 2021 20:25:04 +0300	[thread overview]
Message-ID: <YK6EcMPETjBkVahC@linux.ibm.com> (raw)
In-Reply-To: <20210526130426.GD19992@arm.com>

On Wed, May 26, 2021 at 02:04:26PM +0100, Catalin Marinas wrote:
> On Wed, May 26, 2021 at 12:09:14PM +0000, Qian Cai (QUIC) wrote:
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x0000000090000000-0x0000000091ffffff]
> 
> Maybe de-selecting HOLES_IN_ZONE is not correct for arm64 in all
> circumstances. In a configuration with 64K pages, MAX_ORDER is 14,
> MAX_ORDER_NR_PAGES is 8192, so a 2^29 address range. However, the above
> range starts on 2^28 boundary.
> 
> SECTION_SIZE_BITS is 29 in this configuration but the corresponding
> mem_map[] in the first half of the first section is probably not marked
> as reserved as we'd do for NOMAP.

We do initialize (or at least we should) the first of the first section in
page_alloc::init_unavailable_range() so the range [0x8000000 - 0x9000000]
will have struct pages marked as reserved.

I think it should be fine to de-select HOLES_IN_ZONE as long as MAX_ORDER
chunk does not exceed a section because we do have memory map there in such
case and HOLES_IN_ZONE along with pfn_valid_within() protected against
access to non-existing memory map entries.

We still have an issue with memory map initialization, and probably I've
missed something in decoupling of "do we have memory there" from
pfn_valid().

-- 
Sincerely yours,
Mike.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Mike Rapoport <rppt@linux.ibm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Qian Cai (QUIC)" <quic_qiancai@quicinc.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.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
Date: Wed, 26 May 2021 20:25:04 +0300	[thread overview]
Message-ID: <YK6EcMPETjBkVahC@linux.ibm.com> (raw)
In-Reply-To: <20210526130426.GD19992@arm.com>

On Wed, May 26, 2021 at 02:04:26PM +0100, Catalin Marinas wrote:
> On Wed, May 26, 2021 at 12:09:14PM +0000, Qian Cai (QUIC) wrote:
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x0000000090000000-0x0000000091ffffff]
> 
> Maybe de-selecting HOLES_IN_ZONE is not correct for arm64 in all
> circumstances. In a configuration with 64K pages, MAX_ORDER is 14,
> MAX_ORDER_NR_PAGES is 8192, so a 2^29 address range. However, the above
> range starts on 2^28 boundary.
> 
> SECTION_SIZE_BITS is 29 in this configuration but the corresponding
> mem_map[] in the first half of the first section is probably not marked
> as reserved as we'd do for NOMAP.

We do initialize (or at least we should) the first of the first section in
page_alloc::init_unavailable_range() so the range [0x8000000 - 0x9000000]
will have struct pages marked as reserved.

I think it should be fine to de-select HOLES_IN_ZONE as long as MAX_ORDER
chunk does not exceed a section because we do have memory map there in such
case and HOLES_IN_ZONE along with pfn_valid_within() protected against
access to non-existing memory map entries.

We still have an issue with memory map initialization, and probably I've
missed something in decoupling of "do we have memory there" from
pfn_valid().

-- 
Sincerely yours,
Mike.


  reply	other threads:[~2021-05-26 18:30 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25 15:25 Arm64 crash while reading memory sysfs Qian Cai (QUIC)
2021-05-25 15:25 ` Qian Cai (QUIC)
2021-05-25 15:37 ` David Hildenbrand
2021-05-25 15:37   ` David Hildenbrand
2021-05-26  6:40 ` Mike Rapoport
2021-05-26  6:40   ` Mike Rapoport
2021-05-26 12:09   ` Qian Cai (QUIC)
2021-05-26 12:09     ` Qian Cai (QUIC)
2021-05-26 13:04     ` Catalin Marinas
2021-05-26 13:04       ` Catalin Marinas
2021-05-26 17:25       ` Mike Rapoport [this message]
2021-05-26 17:25         ` Mike Rapoport
2021-05-26 17:24     ` Mike Rapoport
2021-05-26 17:24       ` Mike Rapoport
2021-05-27  0:16       ` Qian Cai
2021-05-27  0:16         ` Qian Cai
2021-05-27  0:31         ` Andrew Morton
2021-05-27  0:31           ` Andrew Morton
2021-05-27  7:25           ` Stephen Rothwell
2021-05-27  7:25             ` Stephen Rothwell
2021-05-27  8:56         ` Mike Rapoport
2021-05-27  8:56           ` Mike Rapoport
2021-05-27 14:33           ` Qian Cai
2021-05-27 14:33             ` Qian Cai
2021-05-27 16:22             ` Mike Rapoport
2021-05-27 16:22               ` Mike Rapoport
2021-05-27 17:00               ` Qian Cai
2021-05-27 17:00                 ` Qian Cai
2021-05-27 17:12               ` David Hildenbrand
2021-05-27 17:12                 ` David Hildenbrand
2021-05-27 17:50               ` Catalin Marinas
2021-05-27 17:50                 ` Catalin Marinas
2021-05-27 22:56                 ` Andrew Morton
2021-05-27 22:56                   ` Andrew Morton
2021-05-28  5:13                   ` Mike Rapoport
2021-05-28  5:13                     ` Mike Rapoport
2021-06-08  7:06                     ` Anshuman Khandual
2021-06-08  7:06                       ` Anshuman Khandual
2021-06-14  8:25                       ` Mike Rapoport
2021-06-14  8:25                         ` Mike Rapoport
2021-06-15  0:13                         ` Andrew Morton
2021-06-15  0:13                           ` Andrew Morton
2021-06-15  6:05                           ` Mike Rapoport
2021-06-15  6:05                             ` Mike Rapoport

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