linux-kernel - [PATCH 1/2] x86,mpx: make mpx depend on x86-64 to free up VMA flag

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Date:   Fri,  4 Aug 2017 15:01:09 -0400
From:   riel@...hat.com
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, fweimer@...hat.com, colm@...costs.net,
        akpm@...ux-foundation.org, rppt@...ux.vnet.ibm.com,
        keescook@...omium.org, luto@...capital.net, wad@...omium.org,
        mingo@...nel.org
Subject: [PATCH 1/2] x86,mpx: make mpx depend on x86-64 to free up VMA flag

From: Rik van Riel <riel@...hat.com>

MPX only seems to be available on 64 bit CPUs, starting with Skylake
and Goldmont. Move VM_MPX into the 64 bit only portion of vma->vm_flags,
in order to free up a VMA flag.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 arch/x86/Kconfig   | 4 +++-
 include/linux/mm.h | 8 ++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 781521b7cf9e..6dff14fadc6f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1756,7 +1756,9 @@ config X86_SMAP
 config X86_INTEL_MPX
 	prompt "Intel MPX (Memory Protection Extensions)"
 	def_bool n
-	depends on CPU_SUP_INTEL
+	# Note: only available in 64-bit mode due to VMA flags shortage
+	depends on CPU_SUP_INTEL && X86_64
+	select ARCH_USES_HIGH_VMA_FLAGS
 	---help---
 	  MPX provides hardware features that can be used in
 	  conjunction with compiler-instrumented code to check
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 46b9ac5e8569..7550eeb06ccf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -208,10 +208,12 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HIGH_ARCH_BIT_1	33	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
 #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
 #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
 #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
+#define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
 #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
 
 #if defined(CONFIG_X86)
@@ -235,9 +237,11 @@ extern unsigned int kobjsize(const void *objp);
 # define VM_MAPPED_COPY	VM_ARCH_1	/* T if mapped copy of data (nommu mmap) */
 #endif
 
-#if defined(CONFIG_X86)
+#if defined(CONFIG_X86_INTEL_MPX)
 /* MPX specific bounds table or bounds directory */
-# define VM_MPX		VM_ARCH_2
+# define VM_MPX		VM_HIGH_ARCH_BIT_4
+#else
+# define VM_MPX		VM_NONE
 #endif
 
 #ifndef VM_GROWSUP
-- 
2.9.4