[PATCH v6 1/3] x86/mm: Add a kernel parameter to change the padding used for the physical memory mapping

[Masayoshi Mizuma]

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

Signed-off-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
---
 arch/x86/include/asm/setup.h |  9 +++++++++
 arch/x86/mm/kaslr.c          | 22 +++++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index ae13bc9..1765a15 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -80,6 +80,15 @@ static inline unsigned long kaslr_offset(void)
 	return (unsigned long)&_text - __START_KERNEL;
 }
 
+#ifdef CONFIG_RANDOMIZE_MEMORY
+extern inline int __init get_rand_mem_physical_padding(void);
+#else
+static inline int __init get_rand_mem_physical_padding(void)
+{
+	return 0;
+}
+#endif
+
 /*
  * Do NOT EVER look at the BIOS memory size location.
  * It does not work on many machines.
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 61db77b..eb47f05 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 rand_mem_physical_padding __initdata = 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 +70,25 @@ static inline bool kaslr_memory_enabled(void)
 	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
 }
 
+inline int __init get_rand_mem_physical_padding(void)
+{
+	return rand_mem_physical_padding;
+}
+
+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 +122,7 @@ 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;
+		get_rand_mem_physical_padding();
 
 	/* Adapt phyiscal memory region size based on available memory */
 	if (memory_tb < kaslr_regions[0].size_tb)
-- 
2.18.0