[tip:x86/boot] x86/mm: Add a kernel parameter to change the padding used for the physical memory mapping

[tip-bot for Masayoshi Mizuma]

Commit-ID:  e79ac9354cf95d75ff6afd341f9c5aa5cbcd638b
Gitweb:     https://git.kernel.org/tip/e79ac9354cf95d75ff6afd341f9c5aa5cbcd638b
Author:     Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
AuthorDate: Mon, 1 Oct 2018 10:08:41 -0400
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 2 Oct 2018 11:47:20 +0200

x86/mm: Add a kernel parameter to change the padding used for the physical memory mapping

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>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20181001140843.26137-2-msys.mizuma@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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..00cf4cae38f5 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;
 
+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)