[RFC] mm: Enable generic pfn_valid() to handle early sections with memmap holes
From: Anshuman Khandual
Date: Sun Mar 07 2021 - 22:28:54 EST
Platforms like arm and arm64 have redefined pfn_valid() because their early
memory sections might have contained memmap holes caused by memblock areas
tagged with MEMBLOCK_NOMAP, which should be skipped while validating a pfn
for struct page backing. This scenario could be captured with a new option
CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES and then generic pfn_valid() can be
improved to accommodate such platforms. This reduces overall code footprint
and also improves maintainability.
Commit 4f5b0c178996 ("arm, arm64: move free_unused_memmap() to generic mm")
had used CONFIG_HAVE_ARCH_PFN_VALID to gate free_unused_memmap(), which in
turn had expanded its scope to new platforms like arc and m68k. Rather lets
restrict back the scope for free_unused_memmap() to arm and arm64 platforms
using this new config option i.e CONFIG_HAVE_EARLY_SECTION_MEMMAP.
While here, it exports the symbol memblock_is_map_memory() to build drivers
that depend on pfn_valid() but does not have the required visibility. After
this new config is in place, just drop CONFIG_HAVE_ARCH_PFN_VALID from both
arm and arm64 platforms.
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
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 applies on 5.12-rc2 along with arm64 pfn_valid() fix patches [1] and
has been lightly tested on the arm64 platform. The idea to represent this
unique situation on the arm and arm64 platforms with a config option was
proposed by David H during an earlier discussion [2]. This still does not
build on arm platform due to pfn_valid() resolution errors. Nonetheless
wanted to get some early feedback whether the overall approach here, is
acceptable or not.
[1] https://patchwork.kernel.org/project/linux-mm/list/?series=442433
[2] https://lore.kernel.org/linux-arm-kernel/4b282848-d2d7-6156-4726-ce974b2dff41@xxxxxxxxxx/
arch/arm/Kconfig | 2 +-
arch/arm/include/asm/page.h | 4 ----
arch/arm/mm/init.c | 13 -----------
arch/arm64/Kconfig | 2 +-
arch/arm64/include/asm/page.h | 2 --
arch/arm64/mm/init.c | 41 -----------------------------------
include/linux/mmzone.h | 24 +++++++++++++++++++-
mm/Kconfig | 10 +++++++++
mm/memblock.c | 3 ++-
9 files changed, 37 insertions(+), 64 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 853aab5ab327..8b1d3089baa6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -71,7 +71,6 @@ config ARM
select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
select HAVE_ARCH_MMAP_RND_BITS if MMU
- select HAVE_ARCH_PFN_VALID
select HAVE_ARCH_SECCOMP
select HAVE_ARCH_SECCOMP_FILTER if AEABI && !OABI_COMPAT
select HAVE_ARCH_THREAD_STRUCT_WHITELIST
@@ -84,6 +83,7 @@ config ARM
select HAVE_DMA_CONTIGUOUS if MMU
select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
+ select HAVE_EARLY_SECTION_MEMMAP_HOLES
select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
select HAVE_EXIT_THREAD
select HAVE_FAST_GUP if ARM_LPAE
diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
index 11b058a72a5b..7e3189083bd7 100644
--- a/arch/arm/include/asm/page.h
+++ b/arch/arm/include/asm/page.h
@@ -153,10 +153,6 @@ extern void copy_page(void *to, const void *from);
typedef struct page *pgtable_t;
-#ifdef CONFIG_HAVE_ARCH_PFN_VALID
-extern int pfn_valid(unsigned long);
-#endif
-
#include <asm/memory.h>
#endif /* !__ASSEMBLY__ */
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 828a2561b229..9131ef4e599e 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -121,19 +121,6 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
free_area_init(max_zone_pfn);
}
-#ifdef CONFIG_HAVE_ARCH_PFN_VALID
-int pfn_valid(unsigned long pfn)
-{
- phys_addr_t addr = __pfn_to_phys(pfn);
-
- if (__phys_to_pfn(addr) != pfn)
- return 0;
-
- return memblock_is_map_memory(addr);
-}
-EXPORT_SYMBOL(pfn_valid);
-#endif
-
static bool arm_memblock_steal_permitted = true;
phys_addr_t __init arm_memblock_steal(phys_addr_t size, phys_addr_t align)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1f212b47a48a..2ee48bdf9dc1 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 012cffc574e8..635a030a3826 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -37,8 +37,6 @@ void copy_highpage(struct page *to, struct page *from);
typedef struct page *pgtable_t;
-extern int pfn_valid(unsigned long);
-
#include <asm/memory.h>
#endif /* !__ASSEMBLY__ */
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 3685e12aba9b..2cba4347aef2 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_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);
-}
-#endif
- return memblock_is_map_memory(addr);
-}
-EXPORT_SYMBOL(pfn_valid);
-
static phys_addr_t memory_limit = PHYS_ADDR_MAX;
/*
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 47946cec7584..93532994113f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1409,8 +1409,23 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
}
#endif
+bool memblock_is_map_memory(phys_addr_t addr);
+
#ifndef CONFIG_HAVE_ARCH_PFN_VALID
static inline 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;
@@ -1423,7 +1438,14 @@ 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_map_memory(pfn << PAGE_SHIFT) : 1;
+
+ return pfn_section_valid(ms, pfn);
+}
+#endif
+ return 1;
}
#endif
diff --git a/mm/Kconfig b/mm/Kconfig
index 24c045b24b95..0ec20f661b3f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -135,6 +135,16 @@ 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 portions which are
+ not backed with struct page mapping as their memblock entries are
+ marked with MEMBLOCK_NOMAP. When subscribed, this option enables
+ specific handling for those memory sections 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 afaefa8fc6ab..d9fa2e62ab7a 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1744,6 +1744,7 @@ bool __init_memblock memblock_is_map_memory(phys_addr_t addr)
return false;
return !memblock_is_nomap(&memblock.memory.regions[i]);
}
+EXPORT_SYMBOL(memblock_is_map_memory);
int __init_memblock memblock_search_pfn_nid(unsigned long pfn,
unsigned long *start_pfn, unsigned long *end_pfn)
@@ -1926,7 +1927,7 @@ static void __init free_unused_memmap(void)
unsigned long start, end, prev_end = 0;
int i;
- if (!IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) ||
+ if (!IS_ENABLED(CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES) ||
IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
return;
--
2.20.1