4 files changed, 39 insertions, 0 deletions

diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 34abae4e9442..b0c7b6c4abda 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -307,3 +307,8 @@ Debugging
                         stuck (default)
 
 Miscellaneous
+
+        nogbpages
+                Do not use GB pages for kernel direct mappings.
+        gbpages
+                Use GB pages for kernel direct mappings.
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 7ce8e7025661..f4413c04e687 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -76,6 +76,18 @@ config DEBUG_RODATA
           data. This is recommended so that we can catch kernel bugs sooner.
           If in doubt, say "Y".
 
+config DIRECT_GBPAGES
+        bool "Enable gbpages-mapped kernel pagetables"
+        depends on DEBUG_KERNEL && EXPERIMENTAL && X86_64
+        help
+          Enable gigabyte pages support (if the CPU supports it). This can
+          improve the kernel's performance a tiny bit by reducing TLB
+          pressure.
+
+          This is experimental code.
+
+          If in doubt, say "N".
+
 config DEBUG_RODATA_TEST
         bool "Testcase for the DEBUG_RODATA feature"
         depends on DEBUG_RODATA
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a02a14f0f324..6e7d5a42a09a 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -54,6 +54,26 @@ static unsigned long dma_reserve __initdata;
 
 DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
 
+int direct_gbpages __meminitdata
+#ifdef CONFIG_DIRECT_GBPAGES
+                                = 1
+#endif
+;
+
+static int __init parse_direct_gbpages_off(char *arg)
+{
+        direct_gbpages = 0;
+        return 0;
+}
+early_param("nogbpages", parse_direct_gbpages_off);
+
+static int __init parse_direct_gbpages_on(char *arg)
+{
+        direct_gbpages = 1;
+        return 0;
+}
+early_param("gbpages", parse_direct_gbpages_on);
+
 /*
  * NOTE: pagetable_init alloc all the fixmap pagetables contiguous on the
  * physical space so we can cache the place of the first one and move
diff --git a/include/asm-x86/pgtable_64.h b/include/asm-x86/pgtable_64.h
index 01d2359e7a34..6ef09914acbe 100644
--- a/include/asm-x86/pgtable_64.h
+++ b/include/asm-x86/pgtable_64.h
@@ -239,6 +239,8 @@ static inline int pud_large(pud_t pte)
 
 #define update_mmu_cache(vma,address,pte) do { } while (0)
 
+extern int direct_gbpages;
+
 /* Encode and de-code a swap entry */
 #define __swp_type(x)                   (((x).val >> 1) & 0x3f)
 #define __swp_offset(x)                 ((x).val >> 8)