Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init

From: Borislav Petkov
Date: Tue Jan 19 2016 - 18:10:56 EST

On Tue, Jan 19, 2016 at 02:57:14PM +0100, Borislav Petkov wrote:
> Patch removing it below.

Andy has a point: I should simply drop static_cpu_has and kill the "_safe"
suffix of the remaining variant:

---
arch/x86/Kconfig.debug | 10 ----
arch/x86/include/asm/cpufeature.h | 99 +++---------------------------------
arch/x86/include/asm/fpu/internal.h | 14 ++---
arch/x86/kernel/apic/apic_numachip.c | 4 +-
arch/x86/kernel/cpu/common.c | 4 +-
arch/x86/kernel/vm86_32.c | 2 +-
drivers/cpufreq/intel_pstate.c | 2 +-
fs/btrfs/disk-io.c | 2 +-
8 files changed, 21 insertions(+), 116 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 9b18ed9..68a2d1f 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -350,16 +350,6 @@ config DEBUG_IMR_SELFTEST

If unsure say N here.

-config X86_DEBUG_STATIC_CPU_HAS
- bool "Debug alternatives"
- depends on DEBUG_KERNEL
- ---help---
- This option causes additional code to be generated which
- fails if static_cpu_has() is used before alternatives have
- run.
-
- If unsure, say N.
-
config X86_DEBUG_FPU
bool "Debug the x86 FPU code"
depends on DEBUG_KERNEL
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 7ad8c94..9219f00 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -406,103 +406,20 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
#define cpu_has_osxsave boot_cpu_has(X86_FEATURE_OSXSAVE)
#define cpu_has_hypervisor boot_cpu_has(X86_FEATURE_HYPERVISOR)
/*
- * Do not add any more of those clumsy macros - use static_cpu_has_safe() for
+ * Do not add any more of those clumsy macros - use static_cpu_has() for
* fast paths and boot_cpu_has() otherwise!
*/

#if __GNUC__ >= 4 && defined(CONFIG_X86_FAST_FEATURE_TESTS)
extern void warn_pre_alternatives(void);
-extern bool __static_cpu_has_safe(u16 bit);
+extern bool __static_cpu_has(u16 bit);

/*
* Static testing of CPU features. Used the same as boot_cpu_has().
* These are only valid after alternatives have run, but will statically
* patch the target code for additional performance.
*/
-static __always_inline __pure bool __static_cpu_has(u16 bit)
-{
-#ifdef CC_HAVE_ASM_GOTO
-
-#ifdef CONFIG_X86_DEBUG_STATIC_CPU_HAS
-
- /*
- * Catch too early usage of this before alternatives
- * have run.
- */
- asm_volatile_goto("1: jmp %l[t_warn]\n"
- "2:\n"
- ".section .altinstructions,\"a\"\n"
- " .long 1b - .\n"
- " .long 0\n" /* no replacement */
- " .word %P0\n" /* 1: do replace */
- " .byte 2b - 1b\n" /* source len */
- " .byte 0\n" /* replacement len */
- " .byte 0\n" /* pad len */
- ".previous\n"
- /* skipping size check since replacement size = 0 */
- : : "i" (X86_FEATURE_ALWAYS) : : t_warn);
-
-#endif
-
- asm_volatile_goto("1: jmp %l[t_no]\n"
- "2:\n"
- ".section .altinstructions,\"a\"\n"
- " .long 1b - .\n"
- " .long 0\n" /* no replacement */
- " .word %P0\n" /* feature bit */
- " .byte 2b - 1b\n" /* source len */
- " .byte 0\n" /* replacement len */
- " .byte 0\n" /* pad len */
- ".previous\n"
- /* skipping size check since replacement size = 0 */
- : : "i" (bit) : : t_no);
- return true;
- t_no:
- return false;
-
-#ifdef CONFIG_X86_DEBUG_STATIC_CPU_HAS
- t_warn:
- warn_pre_alternatives();
- return false;
-#endif
-
-#else /* CC_HAVE_ASM_GOTO */
-
- u8 flag;
- /* Open-coded due to __stringify() in ALTERNATIVE() */
- asm volatile("1: movb $0,%0\n"
- "2:\n"
- ".section .altinstructions,\"a\"\n"
- " .long 1b - .\n"
- " .long 3f - .\n"
- " .word %P1\n" /* feature bit */
- " .byte 2b - 1b\n" /* source len */
- " .byte 4f - 3f\n" /* replacement len */
- " .byte 0\n" /* pad len */
- ".previous\n"
- ".section .discard,\"aw\",@progbits\n"
- " .byte 0xff + (4f-3f) - (2b-1b)\n" /* size check */
- ".previous\n"
- ".section .altinstr_replacement,\"ax\"\n"
- "3: movb $1,%0\n"
- "4:\n"
- ".previous\n"
- : "=qm" (flag) : "i" (bit));
- return flag;
-
-#endif /* CC_HAVE_ASM_GOTO */
-}
-
-#define static_cpu_has(bit) \
-( \
- __builtin_constant_p(boot_cpu_has(bit)) ? \
- boot_cpu_has(bit) : \
- __builtin_constant_p(bit) ? \
- __static_cpu_has(bit) : \
- boot_cpu_has(bit) \
-)
-
-static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
+static __always_inline __pure bool _static_cpu_has(u16 bit)
{
#ifdef CC_HAVE_ASM_GOTO
asm_volatile_goto("1: jmp %l[t_dynamic]\n"
@@ -536,7 +453,7 @@ static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
t_no:
return false;
t_dynamic:
- return __static_cpu_has_safe(bit);
+ return __static_cpu_has(bit);
#else
u8 flag;
/* Open-coded due to __stringify() in ALTERNATIVE() */
@@ -574,22 +491,21 @@ static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
".previous\n"
: "=qm" (flag)
: "i" (bit), "i" (X86_FEATURE_ALWAYS));
- return (flag == 2 ? __static_cpu_has_safe(bit) : flag);
+ return (flag == 2 ? __static_cpu_has(bit) : flag);
#endif /* CC_HAVE_ASM_GOTO */
}

-#define static_cpu_has_safe(bit) \
+#define static_cpu_has(bit) \
( \
__builtin_constant_p(boot_cpu_has(bit)) ? \
boot_cpu_has(bit) : \
- _static_cpu_has_safe(bit) \
+ _static_cpu_has(bit) \
)
#else
/*
* gcc 3.x is too stupid to do the static test; fall back to dynamic.
*/
#define static_cpu_has(bit) boot_cpu_has(bit)
-#define static_cpu_has_safe(bit) boot_cpu_has(bit)
#endif

#define cpu_has_bug(c, bit) cpu_has(c, (bit))
@@ -597,7 +513,6 @@ static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
#define clear_cpu_bug(c, bit) clear_cpu_cap(c, (bit))

#define static_cpu_has_bug(bit) static_cpu_has((bit))
-#define static_cpu_has_bug_safe(bit) static_cpu_has_safe((bit))
#define boot_cpu_has_bug(bit) cpu_has_bug(&boot_cpu_data, (bit))

#define MAX_CPU_FEATURES (NCAPINTS * 32)
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 0fd440d..97022dd 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -58,22 +58,22 @@ extern u64 fpu__get_supported_xfeatures_mask(void);
*/
static __always_inline __pure bool use_eager_fpu(void)
{
- return static_cpu_has_safe(X86_FEATURE_EAGER_FPU);
+ return static_cpu_has(X86_FEATURE_EAGER_FPU);
}

static __always_inline __pure bool use_xsaveopt(void)
{
- return static_cpu_has_safe(X86_FEATURE_XSAVEOPT);
+ return static_cpu_has(X86_FEATURE_XSAVEOPT);
}

static __always_inline __pure bool use_xsave(void)
{
- return static_cpu_has_safe(X86_FEATURE_XSAVE);
+ return static_cpu_has(X86_FEATURE_XSAVE);
}

static __always_inline __pure bool use_fxsr(void)
{
- return static_cpu_has_safe(X86_FEATURE_FXSR);
+ return static_cpu_has(X86_FEATURE_FXSR);
}

/*
@@ -300,7 +300,7 @@ static inline void copy_xregs_to_kernel_booting(struct xregs_state *xstate)

WARN_ON(system_state != SYSTEM_BOOTING);

- if (static_cpu_has_safe(X86_FEATURE_XSAVES))
+ if (static_cpu_has(X86_FEATURE_XSAVES))
XSTATE_OP(XSAVES, xstate, lmask, hmask, err);
else
XSTATE_OP(XSAVE, xstate, lmask, hmask, err);
@@ -322,7 +322,7 @@ static inline void copy_kernel_to_xregs_booting(struct xregs_state *xstate)

WARN_ON(system_state != SYSTEM_BOOTING);

- if (static_cpu_has_safe(X86_FEATURE_XSAVES))
+ if (static_cpu_has(X86_FEATURE_XSAVES))
XSTATE_OP(XRSTORS, xstate, lmask, hmask, err);
else
XSTATE_OP(XRSTOR, xstate, lmask, hmask, err);
@@ -460,7 +460,7 @@ static inline void copy_kernel_to_fpregs(union fpregs_state *fpstate)
* pending. Clear the x87 state here by setting it to fixed values.
* "m" is a random variable that should be in L1.
*/
- if (unlikely(static_cpu_has_bug_safe(X86_BUG_FXSAVE_LEAK))) {
+ if (unlikely(static_cpu_has_bug(X86_BUG_FXSAVE_LEAK))) {
asm volatile(
"fnclex\n\t"
"emms\n\t"
diff --git a/arch/x86/kernel/apic/apic_numachip.c b/arch/x86/kernel/apic/apic_numachip.c
index c80c02c..ab5c2c6 100644
--- a/arch/x86/kernel/apic/apic_numachip.c
+++ b/arch/x86/kernel/apic/apic_numachip.c
@@ -30,7 +30,7 @@ static unsigned int numachip1_get_apic_id(unsigned long x)
unsigned long value;
unsigned int id = (x >> 24) & 0xff;

- if (static_cpu_has_safe(X86_FEATURE_NODEID_MSR)) {
+ if (static_cpu_has(X86_FEATURE_NODEID_MSR)) {
rdmsrl(MSR_FAM10H_NODE_ID, value);
id |= (value << 2) & 0xff00;
}
@@ -178,7 +178,7 @@ static void fixup_cpu_id(struct cpuinfo_x86 *c, int node)
this_cpu_write(cpu_llc_id, node);

/* Account for nodes per socket in multi-core-module processors */
- if (static_cpu_has_safe(X86_FEATURE_NODEID_MSR)) {
+ if (static_cpu_has(X86_FEATURE_NODEID_MSR)) {
rdmsrl(MSR_FAM10H_NODE_ID, val);
nodes = ((val >> 3) & 7) + 1;
}
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 37830de..a57ec0d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1483,11 +1483,11 @@ void warn_pre_alternatives(void)
EXPORT_SYMBOL_GPL(warn_pre_alternatives);
#endif

-inline bool __static_cpu_has_safe(u16 bit)
+inline bool __static_cpu_has(u16 bit)
{
return boot_cpu_has(bit);
}
-EXPORT_SYMBOL_GPL(__static_cpu_has_safe);
+EXPORT_SYMBOL_GPL(__static_cpu_has);

static void bsp_resume(void)
{
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
index e574b85..3dce1ca 100644
--- a/arch/x86/kernel/vm86_32.c
+++ b/arch/x86/kernel/vm86_32.c
@@ -362,7 +362,7 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus)
/* make room for real-mode segments */
tsk->thread.sp0 += 16;

- if (static_cpu_has_safe(X86_FEATURE_SEP))
+ if (static_cpu_has(X86_FEATURE_SEP))
tsk->thread.sysenter_cs = 0;

load_sp0(tss, &tsk->thread);
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index cd83d47..3a4b39a 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1431,7 +1431,7 @@ static int __init intel_pstate_init(void)
if (!all_cpu_data)
return -ENOMEM;

- if (static_cpu_has_safe(X86_FEATURE_HWP) && !no_hwp) {
+ if (static_cpu_has(X86_FEATURE_HWP) && !no_hwp) {
pr_info("intel_pstate: HWP enabled\n");
hwp_active++;
}
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index e99ccd6..87ce612 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -924,7 +924,7 @@ static int check_async_write(struct inode *inode, unsigned long bio_flags)
if (bio_flags & EXTENT_BIO_TREE_LOG)
return 0;
#ifdef CONFIG_X86
- if (static_cpu_has_safe(X86_FEATURE_XMM4_2))
+ if (static_cpu_has(X86_FEATURE_XMM4_2))
return 0;
#endif
return 1;
--
1.8.5.6

SUSE Linux GmbH, GF: Felix ImendÃrffer, Jane Smithard, Graham Norton, HRB 21284 (AG NÃrnberg)
--