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Commit a5fe93a5 authored by yu-cheng yu's avatar yu-cheng yu Committed by Ingo Molnar
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x86/fpu: Disable MPX when eagerfpu is off 



This issue is a fallout from the command-line parsing move.

When "eagerfpu=off" is given as a command-line input, the kernel
should disable MPX support. The decision for turning off MPX was
made in fpu__init_system_ctx_switch(), which is after the
selection of the XSAVE format. This patch fixes it by getting
that decision done earlier in fpu__init_system_xstate().

Signed-off-by: default avatarYu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: yu-cheng yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/1452119094-7252-4-git-send-email-yu-cheng.yu@intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent eb7c5f87

arch/x86/include/asm/fpu/internal.h

+1 −0
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ extern void fpu__init_cpu_xstate(void); 
extern void fpu__init_system(struct cpuinfo_x86 *c);

extern void fpu__init_check_bugs(void);

extern void fpu__resume_cpu(void);

extern u64 fpu__get_supported_xfeatures_mask(void);



/*

 * Debugging facility:

arch/x86/kernel/fpu/init.c

+44 −12
Original line number Diff line number Diff line
@@ -273,8 +273,46 @@ static void __init fpu__init_system_xstate_size_legacy(void) 
 */

static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;



/*

 * Find supported xfeatures based on cpu features and command-line input.

 * This must be called after fpu__init_parse_early_param() is called and

 * xfeatures_mask is enumerated.

 */

u64 __init fpu__get_supported_xfeatures_mask(void)

{

	/* Support all xfeatures known to us */

	if (eagerfpu != DISABLE)

		return XCNTXT_MASK;



	/* Warning of xfeatures being disabled for no eagerfpu mode */

	if (xfeatures_mask & XFEATURE_MASK_EAGER) {

		pr_err("x86/fpu: eagerfpu switching disabled, disabling the following xstate features: 0x%llx.\n",

			xfeatures_mask & XFEATURE_MASK_EAGER);

	}



	/* Return a mask that masks out all features requiring eagerfpu mode */

	return ~XFEATURE_MASK_EAGER;

}



/*

 * Disable features dependent on eagerfpu.

 */

static void __init fpu__clear_eager_fpu_features(void)

{

	setup_clear_cpu_cap(X86_FEATURE_MPX);

}



/*

 * Pick the FPU context switching strategy:

 *

 * When eagerfpu is AUTO or ENABLE, we ensure it is ENABLE if either of

 * the following is true:

 *

 * (1) the cpu has xsaveopt, as it has the optimization and doing eager

 *     FPU switching has a relatively low cost compared to a plain xsave;

 * (2) the cpu has xsave features (e.g. MPX) that depend on eager FPU

 *     switching. Should the kernel boot with noxsaveopt, we support MPX

 *     with eager FPU switching at a higher cost.

 */

static void __init fpu__init_system_ctx_switch(void)

{
@@ -286,19 +324,11 @@ static void __init fpu__init_system_ctx_switch(void) 
	WARN_ON_FPU(current->thread.fpu.fpstate_active);

	current_thread_info()->status = 0;



	/* Auto enable eagerfpu for xsaveopt */

	if (boot_cpu_has(X86_FEATURE_XSAVEOPT) && eagerfpu != DISABLE)

		eagerfpu = ENABLE;



	if (xfeatures_mask & XFEATURE_MASK_EAGER) {

		if (eagerfpu == DISABLE) {

			pr_err("x86/fpu: eagerfpu switching disabled, disabling the following xstate features: 0x%llx.\n",

			       xfeatures_mask & XFEATURE_MASK_EAGER);

			xfeatures_mask &= ~XFEATURE_MASK_EAGER;

		} else {

	if (xfeatures_mask & XFEATURE_MASK_EAGER)

		eagerfpu = ENABLE;

		}

	}



	if (eagerfpu == ENABLE)

		setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
@@ -316,10 +346,12 @@ static void __init fpu__init_parse_early_param(void) 
	 * No need to check "eagerfpu=auto" again, since it is the

	 * initial default.

	 */

	if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off"))

	if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off")) {

		eagerfpu = DISABLE;

	else if (cmdline_find_option_bool(boot_command_line, "eagerfpu=on"))

		fpu__clear_eager_fpu_features();

	} else if (cmdline_find_option_bool(boot_command_line, "eagerfpu=on")) {

		eagerfpu = ENABLE;

	}



	if (cmdline_find_option_bool(boot_command_line, "no387"))

		setup_clear_cpu_cap(X86_FEATURE_FPU);

arch/x86/kernel/fpu/xstate.c

+1 −2
Original line number Diff line number Diff line
@@ -633,8 +633,7 @@ void __init fpu__init_system_xstate(void) 
		BUG();

	}



	/* Support only the state known to the OS: */

	xfeatures_mask = xfeatures_mask & XCNTXT_MASK;

	xfeatures_mask &= fpu__get_supported_xfeatures_mask();



	/* Enable xstate instructions to be able to continue with initialization: */

	fpu__init_cpu_xstate();