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Message-ID: <6096b004-aaeb-d814-87e4-92ec1b180f1d@arm.com>
Date: Thu, 22 Apr 2021 16:53:36 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-mm@...ck.org, david@...hat.com, akpm@...ux-foundation.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections
with memmap holes
On 4/22/21 1:57 PM, Mike Rapoport wrote:
> On Thu, Apr 22, 2021 at 01:20:23PM +0530, Anshuman Khandual wrote:
>> Platforms like arm and arm64 have redefined pfn_valid() because their early
>> memory sections might have contained memmap holes after freeing parts of it
>> during boot, which should be skipped while validating a pfn for struct page
>> backing. This scenario on certain platforms where memmap is not continuous,
>> could be captured with a new option CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES.
>> Then the generic pfn_valid() can be improved to accommodate such platforms.
>> This reduces overall code footprint and also improves maintainability.
>>
>> free_unused_memmap() and pfn_to_online_page() have been updated to include
>> such cases. This also exports memblock_is_memory() for all drivers that use
>> pfn_valid() but lack required visibility. After the new config is in place,
>> drop CONFIG_HAVE_ARCH_PFN_VALID from arm64 platforms.
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Mike Rapoport <rppt@...nel.org>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-kernel@...r.kernel.org
>> Cc: linux-mm@...ck.org
>> Suggested-by: David Hildenbrand <david@...hat.com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>> This patch applies on the latest mainline kernel after Mike's series
>> regarding arm64 based pfn_valid().
>>
>> https://lore.kernel.org/linux-mm/20210422061902.21614-1-rppt@kernel.org/T/#t
>>
>> Changes in RFC V2:
>>
>> - Dropped support for arm (32 bit)
>> - Replaced memblock_is_map_memory() check with memblock_is_memory()
>> - MEMBLOCK_NOMAP memory are no longer skipped for pfn_valid()
>> - Updated pfn_to_online_page() per David
>> - Updated free_unused_memmap() to preserve existing semantics per Mike
>> - Exported memblock_is_memory() instead of memblock_is_map_memory()
>>
>> Changes in RFC V1:
>>
>> - https://patchwork.kernel.org/project/linux-mm/patch/1615174073-10520-1-git-send-email-anshuman.khandual@arm.com/
>>
>> arch/arm64/Kconfig | 2 +-
>> arch/arm64/include/asm/page.h | 1 -
>> arch/arm64/mm/init.c | 41 -----------------------------------
>> include/linux/mmzone.h | 18 ++++++++++++++-
>> mm/Kconfig | 9 ++++++++
>> mm/memblock.c | 8 +++++--
>> mm/memory_hotplug.c | 5 +++++
>> 7 files changed, 38 insertions(+), 46 deletions(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index b4a9b493ce72..4cdc3570ffa9 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -144,7 +144,6 @@ config ARM64
>> select HAVE_ARCH_KGDB
>> select HAVE_ARCH_MMAP_RND_BITS
>> select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>> - select HAVE_ARCH_PFN_VALID
>> select HAVE_ARCH_PREL32_RELOCATIONS
>> select HAVE_ARCH_SECCOMP_FILTER
>> select HAVE_ARCH_STACKLEAK
>> @@ -167,6 +166,7 @@ config ARM64
>> if $(cc-option,-fpatchable-function-entry=2)
>> select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
>> if DYNAMIC_FTRACE_WITH_REGS
>> + select HAVE_EARLY_SECTION_MEMMAP_HOLES
>> select HAVE_EFFICIENT_UNALIGNED_ACCESS
>> select HAVE_FAST_GUP
>> select HAVE_FTRACE_MCOUNT_RECORD
>> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
>> index 75ddfe671393..fcbef3eec4b2 100644
>> --- a/arch/arm64/include/asm/page.h
>> +++ b/arch/arm64/include/asm/page.h
>> @@ -37,7 +37,6 @@ void copy_highpage(struct page *to, struct page *from);
>>
>> typedef struct page *pgtable_t;
>>
>> -int pfn_valid(unsigned long pfn);
>> int pfn_is_map_memory(unsigned long pfn);
>>
>> #include <asm/memory.h>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index f431b38d0837..5731a11550d8 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -217,47 +217,6 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
>> free_area_init(max_zone_pfns);
>> }
>>
>> -int pfn_valid(unsigned long pfn)
>> -{
>> - phys_addr_t addr = PFN_PHYS(pfn);
>> -
>> - /*
>> - * Ensure the upper PAGE_SHIFT bits are clear in the
>> - * pfn. Else it might lead to false positives when
>> - * some of the upper bits are set, but the lower bits
>> - * match a valid pfn.
>> - */
>> - if (PHYS_PFN(addr) != pfn)
>> - return 0;
>> -
>> -#ifdef CONFIG_SPARSEMEM
>> -{
>> - struct mem_section *ms;
>> -
>> - if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>> - return 0;
>> -
>> - ms = __pfn_to_section(pfn);
>> - if (!valid_section(ms))
>> - return 0;
>> -
>> - /*
>> - * ZONE_DEVICE memory does not have the memblock entries.
>> - * memblock_is_memory() check for ZONE_DEVICE based
>> - * addresses will always fail. Even the normal hotplugged
>> - * memory will never have MEMBLOCK_NOMAP flag set in their
>> - * memblock entries. Skip memblock search for all non early
>> - * memory sections covering all of hotplug memory including
>> - * both normal and ZONE_DEVICE based.
>> - */
>> - if (!early_section(ms))
>> - return pfn_section_valid(ms, pfn);
>> -}
>> -#endif
>> - return memblock_is_memory(addr);
>> -}
>> -EXPORT_SYMBOL(pfn_valid);
>> -
>> int pfn_is_map_memory(unsigned long pfn)
>> {
>> phys_addr_t addr = PFN_PHYS(pfn);
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 961f0eeefb62..18bf71665211 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -1421,10 +1421,22 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
>> *
>> * Return: 1 for PFNs that have memory map entries and 0 otherwise
>> */
>> +bool memblock_is_memory(phys_addr_t addr);
>> +
>> static inline int pfn_valid(unsigned long pfn)
>> {
>> + phys_addr_t addr = PFN_PHYS(pfn);
>> struct mem_section *ms;
>>
>> + /*
>> + * Ensure the upper PAGE_SHIFT bits are clear in the
>> + * pfn. Else it might lead to false positives when
>> + * some of the upper bits are set, but the lower bits
>> + * match a valid pfn.
>> + */
>> + if (PHYS_PFN(addr) != pfn)
>> + return 0;
>> +
>> if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>> return 0;
>> ms = __nr_to_section(pfn_to_section_nr(pfn));
>> @@ -1434,7 +1446,11 @@ static inline int pfn_valid(unsigned long pfn)
>> * Traditionally early sections always returned pfn_valid() for
>> * the entire section-sized span.
>> */
>> - return early_section(ms) || pfn_section_valid(ms, pfn);
>> + if (early_section(ms))
>> + return IS_ENABLED(CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES) ?
>> + memblock_is_memory(pfn << PAGE_SHIFT) : 1;
>
> Nit: we already did
>
> addr = PFN_PHYS(pfn);
>
> a few lines above :)
Yeah, will use the addr directly here.
>
>> +
>> + return pfn_section_valid(ms, pfn);
>> }
>> #endif
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 24c045b24b95..db7128111874 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -135,6 +135,15 @@ config HAVE_FAST_GUP
>> config ARCH_KEEP_MEMBLOCK
>> bool
>>
>> +config HAVE_EARLY_SECTION_MEMMAP_HOLES
>> + depends on ARCH_KEEP_MEMBLOCK && SPARSEMEM_VMEMMAP
>> + def_bool n
>> + help
>> + Early sections on certain platforms might have some memory ranges that
>> + are not backed with struct page mappings. When subscribed, this option
>> + enables special handling for those memory ranges in certain situations
>> + such as pfn_valid().
>> +
>> # Keep arch NUMA mapping infrastructure post-init.
>> config NUMA_KEEP_MEMINFO
>> bool
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 3abf2c3fea7f..93f8a9c8428d 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -1740,6 +1740,7 @@ bool __init_memblock memblock_is_memory(phys_addr_t addr)
>> {
>> return memblock_search(&memblock.memory, addr) != -1;
>> }
>> +EXPORT_SYMBOL(memblock_is_memory);
>
> Please make it inside #ifdef CONFIG_ARCH_MEMBLOCK
CONFIG_ARCH_KEEP_MEMBLOCK ? Wrap it around the EXPORT_SYMBOL() or the
entire function memblock_is_memory().
>
>> bool __init_memblock memblock_is_map_memory(phys_addr_t addr)
>> {
>> @@ -1931,8 +1932,11 @@ static void __init free_unused_memmap(void)
>> unsigned long start, end, prev_end = 0;
>> int i;
>>
>> - if (!IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) ||
>> - IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
>> + if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
>> + return;
>> +
>> + if (!IS_ENABLED(CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES) &&
>> + !IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID))
>> return;
>
> Can you please add a comment that says that architecture should provide a
> way to detect holes in the memory map to be able to free its part?
I did not get that completely. If CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES is
not subscribed, then the platform must provide a method that identifies these
memmap holes and process them accordingly in pfn_valid() just to avoid null
pointer dereference ? Also the comment should be placed after the second
return statement, when its going to free unused memmap segments.
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