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Commit 8c3641e9 authored by Dave Hansen's avatar Dave Hansen Committed by Ingo Molnar
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x86/mpx: Introduce a boot-time disable flag 



MPX has the _potential_ to cause some issues.  Say part of your
init system tried to protect one of its components from buffer
overflows with MPX.  If there were a false positive, it's
possible that MPX could keep a system from booting.

MPX could also potentially cause performance issues since it is
present in hot paths like the unmap path.

Allow it to be disabled at boot time.

Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150607183702.2E8B77AB@viggo.jf.intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent eb099e5b

Documentation/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -937,6 +937,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Enable debug messages at boot time.  See

			Documentation/dynamic-debug-howto.txt for details.



	nompx		[X86] Disables Intel Memory Protection Extensions.

			See Documentation/x86/intel_mpx.txt for more

			information about the feature.



	eagerfpu=	[X86]

			on	enable eager fpu restore

			off	disable eager fpu restore

arch/x86/kernel/cpu/common.c

+16 −0
Original line number Diff line number Diff line
@@ -144,6 +144,22 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = { 
} };

EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);



static int __init x86_mpx_setup(char *s)

{

	/* require an exact match without trailing characters */

	if (strlen(s))

		return 0;



	/* do not emit a message if the feature is not present */

	if (!boot_cpu_has(X86_FEATURE_MPX))

		return 1;



	setup_clear_cpu_cap(X86_FEATURE_MPX);

	pr_info("nompx: Intel Memory Protection Extensions (MPX) disabled\n");

	return 1;

}

__setup("nompx", x86_mpx_setup);



#ifdef CONFIG_X86_32

static int cachesize_override = -1;

static int disable_x86_serial_nr = 1;