[PATCH 06/12] x86, pkeys: store protection in high VMA flags

[Dave Hansen]

vma->vm_flags is an 'unsigned long', so has space for 32 flags
on 32-bit architectures.  The high 32 bits are unused on 64-bit
platforms.  We've steered away from using the unused high VMA
bits for things because we would have difficulty supporting it
on 32-bit.

Protection Keys are not available in 32-bit mode, so there is
no concern about supporting this feature in 32-bit mode or on
32-bit CPUs.

This patch carves out 4 bits from the high half of
vma->vm_flags and allows architectures to set config option
to make them available.

---

 b/arch/x86/Kconfig   |    1 +
 b/include/linux/mm.h |    7 +++++++
 b/mm/Kconfig         |    3 +++
 3 files changed, 11 insertions(+)

diff -puN arch/x86/Kconfig~pkeys-7-eat-high-vma-flags arch/x86/Kconfig
--- a/arch/x86/Kconfig~pkeys-7-eat-high-vma-flags	2015-05-07 10:31:42.943257595 -0700
+++ b/arch/x86/Kconfig	2015-05-07 10:31:42.951257956 -0700
@@ -142,6 +142,7 @@ config X86
 	select ACPI_LEGACY_TABLES_LOOKUP if ACPI
 	select X86_FEATURE_NAMES if PROC_FS
 	select SRCU
+	select ARCH_USES_HIGH_VMA_FLAGS if X86_64
 
 config INSTRUCTION_DECODER
 	def_bool y
diff -puN include/linux/mm.h~pkeys-7-eat-high-vma-flags include/linux/mm.h
--- a/include/linux/mm.h~pkeys-7-eat-high-vma-flags	2015-05-07 10:31:42.945257685 -0700
+++ b/include/linux/mm.h	2015-05-07 10:31:42.951257956 -0700
@@ -153,6 +153,13 @@ extern unsigned int kobjsize(const void
 #define VM_NOHUGEPAGE	0x40000000	/* MADV_NOHUGEPAGE marked this vma */
 #define VM_MERGEABLE	0x80000000	/* KSM may merge identical pages */
 
+#ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS
+#define VM_HIGH_ARCH_1  0x100000000	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_2  0x200000000	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_3  0x400000000	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_4  0x800000000	/* bit only usable on 64-bit architectures */
+#endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
+
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
 #elif defined(CONFIG_PPC)
diff -puN mm/Kconfig~pkeys-7-eat-high-vma-flags mm/Kconfig
--- a/mm/Kconfig~pkeys-7-eat-high-vma-flags	2015-05-07 10:31:42.947257775 -0700
+++ b/mm/Kconfig	2015-05-07 10:31:42.952258001 -0700
@@ -635,3 +635,6 @@ config MAX_STACK_SIZE_MB
 	  changed to a smaller value in which case that is used.
 
 	  A sane initial value is 80 MB.
+
+config ARCH_USES_HIGH_VMA_FLAGS
+	bool
_
--
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