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Subject[RFC PATCH v3 1/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory
Date
mhp_supports_memmap_on_memory is meant to be used by the caller prior
to hot-adding memory in order to figure out whether it can enable
MHP_MEMMAP_ON_MEMORY or not.

Enabling MHP_MEMMAP_ON_MEMORY requires:

- memmap_on_memory_enabled is set (by mhp_memmap_on_memory kernel boot option)
- CONFIG_SPARSEMEM_VMEMMAP
- architecture support for altmap
- hot-added range spans a single memory block

Note that mhp_memmap_on_memory kernel boot option will be added in
a coming patch.

At the moment, only three architectures support passing altmap when
building the page tables: x86, POWERPC and ARM.
Define an arch_support_memmap_on_memory function on those architectures
that returns true, and define a __weak variant of it that will be used
on the others.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
arch/arm64/mm/mmu.c | 5 +++++
arch/powerpc/mm/mem.c | 5 +++++
arch/x86/mm/init_64.c | 5 +++++
include/linux/memory_hotplug.h | 10 ++++++++++
mm/memory_hotplug.c | 24 ++++++++++++++++++++++++
5 files changed, 49 insertions(+)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 30c6dd02e706..8a33ac97dcbb 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1454,6 +1454,11 @@ static bool inside_linear_region(u64 start, u64 size)
(start + size - 1) <= __pa(PAGE_END - 1);
}

+bool arch_support_memmap_on_memory(void)
+{
+ return true;
+}
+
int arch_add_memory(int nid, u64 start, u64 size,
struct mhp_params *params)
{
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 0694bdcce653..c5ef015c3189 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -181,6 +181,11 @@ void __ref arch_remove_memory(int nid, u64 start, u64 size,
__remove_pages(start_pfn, nr_pages, altmap);
arch_remove_linear_mapping(start, size);
}
+
+bool arch_support_memmap_on_memory(void)
+{
+ return true;
+}
#endif

#ifndef CONFIG_NEED_MULTIPLE_NODES
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index b5a3fa4033d3..ffb9d87c77e8 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -860,6 +860,11 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
return ret;
}

+bool arch_support_memmap_on_memory(void)
+{
+ return true;
+}
+
int arch_add_memory(int nid, u64 start, u64 size,
struct mhp_params *params)
{
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 15acce5ab106..a54310abee79 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -70,6 +70,14 @@ typedef int __bitwise mhp_t;
*/
#define MEMHP_MERGE_RESOURCE ((__force mhp_t)BIT(0))

+/*
+ * We want memmap (struct page array) to be self contained.
+ * To do so, we will use the beginning of the hot-added range to build
+ * the page tables for the memmap array that describes the entire range.
+ * Only selected architectures support it with SPARSE_VMEMMAP.
+ */
+#define MHP_MEMMAP_ON_MEMORY ((__force mhp_t)BIT(1))
+
/*
* Extended parameters for memory hotplug:
* altmap: alternative allocator for memmap array (optional)
@@ -129,6 +137,7 @@ extern int try_online_node(int nid);

extern int arch_add_memory(int nid, u64 start, u64 size,
struct mhp_params *params);
+extern bool arch_support_memmap_on_memory(void);
extern u64 max_mem_size;

extern int memhp_online_type_from_str(const char *str);
@@ -361,6 +370,7 @@ extern struct page *sparse_decode_mem_map(unsigned long coded_mem_map,
unsigned long pnum);
extern struct zone *zone_for_pfn_range(int online_type, int nid, unsigned start_pfn,
unsigned long nr_pages);
+extern bool mhp_supports_memmap_on_memory(unsigned long size);
extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
struct mhp_params *params);
void arch_remove_linear_mapping(u64 start, u64 size);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a8cef4955907..e3c310225a60 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1011,6 +1011,20 @@ static int online_memory_block(struct memory_block *mem, void *arg)
return device_online(&mem->dev);
}

+bool __weak arch_support_memmap_on_memory(void)
+{
+ return false;
+}
+
+bool mhp_supports_memmap_on_memory(unsigned long size)
+{
+ if (!arch_support_memmap_on_memory() ||
+ !IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) ||
+ size > memory_block_size_bytes())
+ return false;
+ return true;
+}
+
/*
* NOTE: The caller must call lock_device_hotplug() to serialize hotplug
* and online/offline operations (triggered e.g. by sysfs).
@@ -1046,6 +1060,16 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
goto error;
new_node = ret;

+ /*
+ * Return -EINVAL if caller specified MHP_MEMMAP_ON_MEMORY and we do
+ * not support it.
+ */
+ if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
+ !mhp_supports_memmap_on_memory(size)) {
+ ret = -EINVAL;
+ goto error;
+ }
+
/* call arch's memory hotadd */
ret = arch_add_memory(nid, start, size, &params);
if (ret < 0)
--
2.26.2
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