From: David Hildenbrand <david@redhat.com>
To: Mike Rapoport <rppt@kernel.org>, mawupeng <mawupeng1@huawei.com>
Cc: ardb@kernel.org, corbet@lwn.net, will@kernel.org,
catalin.marinas@arm.com, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
hpa@zytor.com, dvhart@infradead.org, andy@infradead.org,
akpm@linux-foundation.org, paul.walmsley@sifive.com,
palmer@dabbelt.com, aou@eecs.berkeley.edu, paulmck@kernel.org,
keescook@chromium.org, songmuchun@bytedance.com,
rdunlap@infradead.org, damien.lemoal@opensource.wdc.com,
swboyd@chromium.org, wei.liu@kernel.org, robin.murphy@arm.com,
anshuman.khandual@arm.com, thunder.leizhen@huawei.com,
wangkefeng.wang@huawei.com, gpiccoli@igalia.com,
chenhuacai@kernel.org, geert@linux-m68k.org,
chenzhou10@huawei.com, vijayb@linux.microsoft.com,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-efi@vger.kernel.org,
platform-driver-x86@vger.kernel.org, linux-mm@kvack.org,
linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3 5/6] mm: Add mirror flag back on initrd memory
Date: Wed, 8 Jun 2022 12:08:20 +0200 [thread overview]
Message-ID: <cd0e727d-8ad6-2d74-55f5-498394aae297@redhat.com> (raw)
In-Reply-To: <YqBzwgTgWEAx8J/C@kernel.org>
On 08.06.22 12:02, Mike Rapoport wrote:
> On Wed, Jun 08, 2022 at 03:27:09PM +0800, mawupeng wrote:
>>
>> 在 2022/6/7 22:49, Ard Biesheuvel 写道:
>>> On Tue, 7 Jun 2022 at 14:22, David Hildenbrand <david@redhat.com> wrote:
>>>>
>>>> On 07.06.22 11:38, Wupeng Ma wrote:
>>>>> From: Ma Wupeng <mawupeng1@huawei.com>
>>>>>
>>>>> Initrd memory will be removed and then added in arm64_memblock_init() and this
>>>>> will cause it to lose all of its memblock flags. The lost of MEMBLOCK_MIRROR
>>>>> flag will lead to error log printed by find_zone_movable_pfns_for_nodes if
>>>>> the lower 4G range has some non-mirrored memory.
>>>>>
>>>>> In order to solve this problem, the lost MEMBLOCK_MIRROR flag will be
>>>>> reinstalled if the origin memblock has this flag.
>>>>>
>>>>> Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
>>>>> ---
>>>>> arch/arm64/mm/init.c | 9 +++++++++
>>>>> include/linux/memblock.h | 1 +
>>>>> mm/memblock.c | 20 ++++++++++++++++++++
>>>>> 3 files changed, 30 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>>>> index 339ee84e5a61..11641f924d08 100644
>>>>> --- a/arch/arm64/mm/init.c
>>>>> +++ b/arch/arm64/mm/init.c
>>>>> @@ -350,9 +350,18 @@ void __init arm64_memblock_init(void)
>>>>> "initrd not fully accessible via the linear mapping -- please check your bootloader ...\n")) {
>>>>> phys_initrd_size = 0;
>>>>> } else {
>>>>> + int flags, ret;
>>>>> +
>>>>> + ret = memblock_get_flags(base, &flags);
>>>>> + if (ret)
>>>>> + flags = 0;
>>>>> +
>>>>> memblock_remove(base, size); /* clear MEMBLOCK_ flags */
>>>>> memblock_add(base, size);
>>>>> memblock_reserve(base, size);
>>>>
>>>> Can you explain why we're removing+re-adding here exactly? Is it just to
>>>> clear flags as the comment indicates?
>>>>
>>>
>>> This should only happen if the placement of the initrd conflicts with
>>> a mem= command line parameter or it is not covered by memblock for
>>> some other reason.
>>>
>>> IOW, this should never happen, and if re-memblock_add'ing this memory
>>> unconditionally is causing problems, we should fix that instead of
>>> working around it.
>>
>> This will happen if we use initrdmem=3G,100M to reserve initrd memory below
>> the 4G limit to test this scenario(just for testing, I have trouble to boot
>> qemu with initrd enabled and memory below 4G are all mirror memory).
>>
>> Re-memblock_add'ing this memory unconditionally seems fine but clear all
>> flags(especially MEMBLOCK_MIRROR) may lead to some error log.
>>
>>>
>>>> If it's really just about clearing flags, I wonder if we rather want to
>>>> have an interface that does exactly that, and hides the way this is
>>>> actually implemented (obtain flags, remove, re-add ...), internally.
>>>>
>>>> But most probably there is more magic in the code and clearing flags
>>>> isn't all it ends up doing.
>>>>
>>>
>>> I don't remember exactly why we needed to clear the flags, but I think
>>> it had to do with some corner case we hit when the initrd was
>>> partially covered.
>> If "mem=" is set in command line, memblock_mem_limit_remove_map() will
>> remove all memory block without MEMBLOCK_NOMAP. Maybe this will bring the
>> memory back if this initrd mem has the MEMBLOCK_NOMAP flag?
>>
>> The rfc version [1] introduce and use memblock_clear_nomap() to clear the
>> MEMBLOCK_NOMAP of this initrd memblock.
>> So maybe the usage of memblock_remove() is just to avoid introducing new
>> function(memblock_clear_nomap)?
>>
>> Since commit 4c546b8a3469 ("memblock: add memblock_clear_nomap()") already
>> introduced memblock_clear_nomap(). Can we use this to remove flag MEMBLOCK_NOMAP
>> to solve this problem rather than bring flag MEMBLOCK_MIRROR back?
>
> AFAICT, there are two corner cases that re-adding initrd memory covers:
> * initrd memory is not a part of the memory reported to memblock, either
> because of firmware weirdness or because it was cut out with mem=
> * initrd memory overlaps a NOMAP region
>
> So to make sure initrd memory is mapped properly and retains
> MEMBLOCK_MIRROR I think the best we can do is
>
> memblock_add();
> memblock_clear_nomap();
> memblock_reserve();
Would simply detect+rejecting to boot on such setups be an option? The
replies so far indicate to me that this is rather a corner case than a
reasonable use case.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-06-08 10:21 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-07 9:37 [PATCH v3 0/6] introduce mirrored memory support for arm64 Wupeng Ma
2022-06-07 9:38 ` [PATCH v3 1/6] efi: Make efi_find_mirror() public Wupeng Ma
2022-06-10 9:22 ` Kefeng Wang
2022-06-07 9:38 ` [PATCH v3 2/6] arm64/mirror: arm64 enabling - find mirrored memory ranges Wupeng Ma
2022-06-10 9:27 ` Kefeng Wang
2022-06-10 9:34 ` Ard Biesheuvel
2022-06-10 10:24 ` Kefeng Wang
2022-06-10 11:17 ` Ard Biesheuvel
2022-06-07 9:38 ` [PATCH v3 3/6] mm: Ratelimited mirrored memory related warning messages Wupeng Ma
2022-06-07 12:24 ` David Hildenbrand
2022-06-08 9:44 ` Mike Rapoport
2022-06-08 10:02 ` Anshuman Khandual
2022-06-10 9:29 ` Kefeng Wang
2022-06-07 9:38 ` [PATCH v3 4/6] mm: Demote warning message in vmemmap_verify() to debug level Wupeng Ma
2022-06-07 12:25 ` David Hildenbrand
2022-06-08 1:26 ` mawupeng
2022-06-08 10:00 ` Anshuman Khandual
2022-06-09 8:13 ` mawupeng
2022-06-10 9:35 ` Kefeng Wang
2022-06-07 9:38 ` [PATCH v3 5/6] mm: Add mirror flag back on initrd memory Wupeng Ma
2022-06-07 12:21 ` David Hildenbrand
2022-06-07 14:49 ` Ard Biesheuvel
2022-06-08 7:27 ` mawupeng
2022-06-08 10:02 ` Mike Rapoport
2022-06-08 10:08 ` David Hildenbrand [this message]
2022-06-08 10:12 ` Ard Biesheuvel
2022-06-09 8:15 ` mawupeng
2022-06-10 11:06 ` Ard Biesheuvel
2022-06-07 9:38 ` [PATCH v3 6/6] efi: Disable mirror feature if kernelcore is not specified Wupeng Ma
2022-06-10 11:20 ` Ard Biesheuvel
2022-06-10 12:15 ` Kefeng Wang
2022-06-10 11:23 ` [PATCH v3 0/6] introduce mirrored memory support for arm64 Ard Biesheuvel
2022-06-10 11:24 ` Ard Biesheuvel
2022-06-11 9:56 ` Mike Rapoport
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