On 08.03.21 04:27, Anshuman Khandual wrote:
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.
It might make sense to keep the arm variant for now. The arm64 variant
is where the magic happens and where we missed updates when working on
the generic variant.
The generic variant really only applies to 64bit targets where we have
SPARSEMEM. See x86 as an example.
[...]
/*
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;
I think this should be fine for other archs as well.
+
+#ifdef CONFIG_SPARSEMEM
Why do we need the ifdef now? If that's to cover the arm case, then
please consider the arm64 case only for now.
{
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;
With
commit 1f90a3477df3ff1a91e064af554cdc887c8f9e5e
Author: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Thu Feb 25 17:17:05 2021 -0800
mm: teach pfn_to_online_page() about ZONE_DEVICE section collisions
(still in -next I think)
You'll also have to take care of pfn_to_online_page().
--
Thanks,
David / dhildenb
