Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes

From: Mike Rapoport
Date: Tue May 25 2021 - 06:03:25 EST

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On Tue, May 25, 2021 at 03:22:53PM +0530, Anshuman Khandual wrote:
>
>
> On 5/25/21 12:02 PM, Mike Rapoport wrote:
> > On Tue, May 25, 2021 at 11:30:15AM +0530, Anshuman Khandual wrote:
> >>
> >> On 5/24/21 12:22 PM, Mike Rapoport wrote:
> >>> Hello Anshuman,
> >>>
> >>> On Mon, May 24, 2021 at 10:28:32AM +0530, Anshuman Khandual wrote:
> >>>>
> >>>> On 4/22/21 1:20 PM, 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@xxxxxxx>
> >>>>> Cc: Will Deacon <will@xxxxxxxxxx>
> >>>>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >>>>> Cc: Mike Rapoport <rppt@xxxxxxxxxx>
> >>>>> Cc: David Hildenbrand <david@xxxxxxxxxx>
> >>>>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> >>>>> Cc: linux-kernel@xxxxxxxxxxxxxxx
> >>>>> Cc: linux-mm@xxxxxxxxx
> >>>>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> >>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> >>>>> ---
> >>>>> 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@xxxxxxxxxx/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@xxxxxxx/
> >>>>>
> >>>>> 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;
> >>>>> +
> >>>>> + return pfn_section_valid(ms, pfn);
> >>>>> }
> >>>>> #endif
> >>>>
> >>>> Hello David/Mike,
> >>>>
> >>>> Now that pfn_is_map_memory() usage has been decoupled from pfn_valid() and
> >>>> SPARSEMEM_VMEMMAP is only available memory model on arm64, wondering if we
> >>>> still need this HAVE_EARLY_SECTION_MEMMAP_HOLES proposal ? Please do kindly
> >>>> suggest. Thank you.
> >>>
> >>> Even now arm64 still frees parts of the memory map and pfn_valid() should
> >>> be able to tell if a part of a section is freed or not.
> >>>
> >>> For instance for the following memory configuration
> >>>
> >>> |<----section---->|<----hole---->|<----section---->|
> >>> +--------+--------+--------------+--------+--------+
> >>> | bank 0 | unused | | bank 1 | unused |
> >>> +--------+--------+--------------+--------+--------+
> >>>
> >>> the memory map corresponding to the "unused" areas is freed, but the generic
> >>> pfn_valid() will still return 1 there.
> >>
> >> But is not free_unused_memmap() return early when CONFIG_SPARSEMEM_VMEMMAP
> >> is enabled, which is the only option now on arm64. Then how can memmap have
> >> holes (from unused areas) anymore ? Am I missing something here.
> >
> > Ah, you are right, I missed this detail myself :)
> >
> > With CONFIG_SPARSEMEM_VMEMMAP as the only memory model for arm64, we can
> > simply rid of arm64::pfn_valid() without any changes to the generic
> > version.
>
> Though just moved the pfn bits sanity check into generic pfn_valid().
> I hope this looks okay.
>
> From 7a63f460bcb6ae171c2081bfad81edd9e8f3b7a0 Mon Sep 17 00:00:00 2001
> From: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Date: Tue, 25 May 2021 10:27:09 +0100
> Subject: [PATCH] arm64/mm: Drop HAVE_ARCH_PFN_VALID
>
> CONFIG_SPARSEMEM_VMEMMAP is now the only available memory model on arm64
> platforms and free_unused_memmap() would just return without creating any
> holes in the memmap mapping. There is no need for any special handling in
> pfn_valid() and HAVE_ARCH_PFN_VALID can just be dropped. This also moves
> the pfn upper bits sanity check into generic pfn_valid().
>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>

> ---
> arch/arm64/Kconfig | 1 -
> arch/arm64/include/asm/page.h | 1 -
> arch/arm64/mm/init.c | 37 -----------------------------------
> include/linux/mmzone.h | 9 +++++++++
> 4 files changed, 9 insertions(+), 39 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index d7dc8698cf8e..7904728befcc 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -154,7 +154,6 @@ 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_RANDOMIZE_KSTACK_OFFSET
> select HAVE_ARCH_SECCOMP_FILTER
> 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 725aa84f2faa..49019ea0c8a8 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -219,43 +219,6 @@ 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);
> - 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 = __pfn_to_section(pfn);
> - if (!valid_section(ms))
> - return 0;
> -
> - /*
> - * ZONE_DEVICE memory does not have the memblock entries.
> - * memblock_is_map_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);
> -
> - 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 a9b263d4cf9d..d0c4fc506fa3 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1443,6 +1443,15 @@ static inline int pfn_valid(unsigned long 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(PFN_PHYS(pfn)) != pfn)
> + return 0;
> +
> if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> return 0;
> ms = __nr_to_section(pfn_to_section_nr(pfn));
> --
> 2.20.1

--
Sincerely yours,
Mike.

Next message: Thomas Zimmermann: "Re: [PATCH v5 0/3] Add option to mmap GEM buffers cached"
Previous message: Jonathan Cameron: "Re: [PATCH v2 4/5] cxl/mem: Reserve individual register block regions"
In reply to: Anshuman Khandual: "Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes"
Next in thread: David Hildenbrand: "Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes"
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