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Message-ID: <dfa5fc60-eddc-1359-7a5f-a5c3a1d8a25b@arm.com>
Date: Tue, 25 May 2021 15:22:53 +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 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@....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;
>>>>> +
>>>>> + 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@....com>
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@....com>
---
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
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