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x86/fpu: Disable MPX when eagerfpu is off

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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: Yu-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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
yu-cheng yu 2016-01-06 14:24:53 -08:00 committed by Ingo Molnar
parent eb7c5f872e
commit a5fe93a549
3 changed files with 46 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/fpu/internal.h
View File

@ -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:

56
arch/x86/kernel/fpu/init.c
View File

@ -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 {
eagerfpu = ENABLE;
}
}
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);

3
arch/x86/kernel/fpu/xstate.c
View File

@ -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();