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Subject[PATCH v3 1/2] x86/mm: Add an option to change the padding used for the physical memory mapping
Date
From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

If each node of physical memory layout has huge space for hotplug,
the padding used for the physical memory mapping section is not enough.
For exapmle of the layout:
SRAT: Node 6 PXM 4 [mem 0x100000000000-0x13ffffffffff] hotplug
SRAT: Node 7 PXM 5 [mem 0x140000000000-0x17ffffffffff] hotplug
SRAT: Node 2 PXM 6 [mem 0x180000000000-0x1bffffffffff] hotplug
SRAT: Node 3 PXM 7 [mem 0x1c0000000000-0x1fffffffffff] hotplug

We can increase the padding by CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING,
however, the needed padding size depends on the system environment.
The kernel option is better than changing the config.

Change log from v2:
- Simplify the description. As Baoquan said, this is simillar SGI UV issue,
but a little different. Remove SGI UV description.

Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
---
arch/x86/mm/kaslr.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 61db77b0eda9..aeb62615bd46 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -40,6 +40,7 @@
*/
static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;

+static int __initdata rand_mem_physical_padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
/*
* Memory regions randomized by KASLR (except modules that use a separate logic
* earlier during boot). The list is ordered based on virtual addresses. This
@@ -69,6 +70,20 @@ static inline bool kaslr_memory_enabled(void)
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}

+static int __init rand_mem_physical_padding_setup(char *str)
+{
+ int max_padding = (1 << (MAX_PHYSMEM_BITS - TB_SHIFT)) - 1;
+
+ get_option(&str, &rand_mem_physical_padding);
+ if (rand_mem_physical_padding < 0)
+ rand_mem_physical_padding = 0;
+ else if (rand_mem_physical_padding > max_padding)
+ rand_mem_physical_padding = max_padding;
+
+ return 0;
+}
+early_param("rand_mem_physical_padding", rand_mem_physical_padding_setup);
+
/* Initialize base and padding for each memory region randomized with KASLR */
void __init kernel_randomize_memory(void)
{
@@ -102,7 +117,7 @@ void __init kernel_randomize_memory(void)
*/
BUG_ON(kaslr_regions[0].base != &page_offset_base);
memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
- CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+ rand_mem_physical_padding;

/* Adapt phyiscal memory region size based on available memory */
if (memory_tb < kaslr_regions[0].size_tb)
--
2.18.0
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