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[2003:cb:c705:ad00:db2:4c6:8f3a:2ec4]) by smtp.gmail.com with ESMTPSA id x4-20020adfffc4000000b0021018642ff8sm20678946wrs.76.2022.06.08.03.08.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jun 2022 03:08:23 -0700 (PDT) Message-ID: Date: Wed, 8 Jun 2022 12:08:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v3 5/6] mm: Add mirror flag back on initrd memory Content-Language: en-US To: Mike Rapoport , mawupeng 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 References: <20220607093805.1354256-1-mawupeng1@huawei.com> <20220607093805.1354256-6-mawupeng1@huawei.com> <99900b31-2605-2c85-a1b7-9ef2666b58da@redhat.com> <29900b05-ec44-76a2-645a-22a13399d7fd@huawei.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.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 wrote: >>>> >>>> On 07.06.22 11:38, Wupeng Ma wrote: >>>>> From: Ma Wupeng >>>>> >>>>> 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 >>>>> --- >>>>> 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