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Subject[PATCH 1/3] x86, fpu: decouple non-lazy/eager fpu restore from xsave
Date
Decouple non-lazy/eager fpu restore policy from the existence of the xsave
feature. Introduce a synthetic CPUID flag to represent the eagerfpu
policy. "eagerfpu=on" boot paramter will enable the policy.

Requested-by: H. Peter Anvin <hpa@zytor.com>
Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
Documentation/kernel-parameters.txt | 4 ++
arch/x86/include/asm/cpufeature.h | 2 +
arch/x86/include/asm/fpu-internal.h | 54 ++++++++++++++++------
arch/x86/kernel/cpu/common.c | 2 -
arch/x86/kernel/i387.c | 25 +++-------
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/traps.c | 2 +-
arch/x86/kernel/xsave.c | 87 +++++++++++++++++++++++------------
8 files changed, 112 insertions(+), 66 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a92c5eb..6273099 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1834,6 +1834,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
and restore using xsave. The kernel will fallback to
enabling legacy floating-point and sse state.

+ eagerfpu= [X86]
+ on enable eager fpu restore
+ off disable eager fpu restore
+
nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
wfi(ARM) instruction doesn't work correctly and not to
use it. This is also useful when using JTAG debugger.
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 340ee49..eb9f8d1 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -97,6 +97,7 @@
#define X86_FEATURE_EXTD_APICID (3*32+26) /* has extended APICID (8 bits) */
#define X86_FEATURE_AMD_DCM (3*32+27) /* multi-node processor */
#define X86_FEATURE_APERFMPERF (3*32+28) /* APERFMPERF */
+#define X86_FEATURE_EAGER_FPU (3*32+29) /* "eagerfpu" Non lazy FPU restore */

/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* "pni" SSE-3 */
@@ -303,6 +304,7 @@ extern const char * const x86_power_flags[32];
#define cpu_has_perfctr_core boot_cpu_has(X86_FEATURE_PERFCTR_CORE)
#define cpu_has_cx8 boot_cpu_has(X86_FEATURE_CX8)
#define cpu_has_cx16 boot_cpu_has(X86_FEATURE_CX16)
+#define cpu_has_eager_fpu boot_cpu_has(X86_FEATURE_EAGER_FPU)

#if defined(CONFIG_X86_INVLPG) || defined(CONFIG_X86_64)
# define cpu_has_invlpg 1
diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index e31cc6e..df023b4 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -38,6 +38,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka,

extern unsigned int mxcsr_feature_mask;
extern void fpu_init(void);
+extern void eager_fpu_init(void);

DECLARE_PER_CPU(struct task_struct *, fpu_owner_task);

@@ -84,6 +85,11 @@ static inline int is_x32_frame(void)

#define X87_FSW_ES (1 << 7) /* Exception Summary */

+static __always_inline __pure bool use_eager_fpu(void)
+{
+ return static_cpu_has(X86_FEATURE_EAGER_FPU);
+}
+
static __always_inline __pure bool use_xsaveopt(void)
{
return static_cpu_has(X86_FEATURE_XSAVEOPT);
@@ -99,6 +105,14 @@ static __always_inline __pure bool use_fxsr(void)
return static_cpu_has(X86_FEATURE_FXSR);
}

+static inline void fx_finit(struct i387_fxsave_struct *fx)
+{
+ memset(fx, 0, xstate_size);
+ fx->cwd = 0x37f;
+ if (cpu_has_xmm)
+ fx->mxcsr = MXCSR_DEFAULT;
+}
+
extern void __sanitize_i387_state(struct task_struct *);

static inline void sanitize_i387_state(struct task_struct *tsk)
@@ -291,13 +305,13 @@ static inline void __thread_set_has_fpu(struct task_struct *tsk)
static inline void __thread_fpu_end(struct task_struct *tsk)
{
__thread_clear_has_fpu(tsk);
- if (!use_xsave())
+ if (!use_eager_fpu())
stts();
}

static inline void __thread_fpu_begin(struct task_struct *tsk)
{
- if (!use_xsave())
+ if (!use_eager_fpu())
clts();
__thread_set_has_fpu(tsk);
}
@@ -327,10 +341,14 @@ static inline void drop_fpu(struct task_struct *tsk)

static inline void drop_init_fpu(struct task_struct *tsk)
{
- if (!use_xsave())
+ if (!use_eager_fpu())
drop_fpu(tsk);
- else
- xrstor_state(init_xstate_buf, -1);
+ else {
+ if (use_xsave())
+ xrstor_state(init_xstate_buf, -1);
+ else
+ fxrstor_checking(&init_xstate_buf->i387);
+ }
}

/*
@@ -370,7 +388,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
* If the task has used the math, pre-load the FPU on xsave processors
* or if the past 5 consecutive context-switches used math.
*/
- fpu.preload = tsk_used_math(new) && (use_xsave() ||
+ fpu.preload = tsk_used_math(new) && (use_eager_fpu() ||
new->fpu_counter > 5);
if (__thread_has_fpu(old)) {
if (!__save_init_fpu(old))
@@ -383,14 +401,14 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
new->fpu_counter++;
__thread_set_has_fpu(new);
prefetch(new->thread.fpu.state);
- } else if (!use_xsave())
+ } else if (!use_eager_fpu())
stts();
} else {
old->fpu_counter = 0;
old->thread.fpu.last_cpu = ~0;
if (fpu.preload) {
new->fpu_counter++;
- if (!use_xsave() && fpu_lazy_restore(new, cpu))
+ if (!use_eager_fpu() && fpu_lazy_restore(new, cpu))
fpu.preload = 0;
else
prefetch(new->thread.fpu.state);
@@ -452,6 +470,14 @@ static inline void user_fpu_begin(void)
preempt_enable();
}

+static inline void __save_fpu(struct task_struct *tsk)
+{
+ if (use_xsave())
+ xsave_state(&tsk->thread.fpu.state->xsave, -1);
+ else
+ fpu_fxsave(&tsk->thread.fpu);
+}
+
/*
* These disable preemption on their own and are safe
*/
@@ -459,8 +485,8 @@ static inline void save_init_fpu(struct task_struct *tsk)
{
WARN_ON_ONCE(!__thread_has_fpu(tsk));

- if (use_xsave()) {
- xsave_state(&tsk->thread.fpu.state->xsave, -1);
+ if (use_eager_fpu()) {
+ __save_fpu(tsk);
return;
}

@@ -526,11 +552,9 @@ static inline void fpu_free(struct fpu *fpu)

static inline void fpu_copy(struct task_struct *dst, struct task_struct *src)
{
- if (use_xsave()) {
- struct xsave_struct *xsave = &dst->thread.fpu.state->xsave;
-
- memset(&xsave->xsave_hdr, 0, sizeof(struct xsave_hdr_struct));
- xsave_state(xsave, -1);
+ if (use_eager_fpu()) {
+ memset(&dst->thread.fpu.state->xsave, 0, xstate_size);
+ __save_fpu(dst);
} else {
struct fpu *dfpu = &dst->thread.fpu;
struct fpu *sfpu = &src->thread.fpu;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6b9333b..db7dd8f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1264,7 +1264,6 @@ void __cpuinit cpu_init(void)
dbg_restore_debug_regs();

fpu_init();
- xsave_init();

raw_local_save_flags(kernel_eflags);

@@ -1319,6 +1318,5 @@ void __cpuinit cpu_init(void)
dbg_restore_debug_regs();

fpu_init();
- xsave_init();
}
#endif
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 5285574..6782e39 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -22,9 +22,8 @@
/*
* Were we in an interrupt that interrupted kernel mode?
*
- * For now, on xsave platforms we will return interrupted
- * kernel FPU as not-idle. TBD: As we use non-lazy FPU restore
- * for xsave platforms, ideally we can change the return value
+ * For now, with eagerfpu we will return interrupted kernel FPU
+ * state as not-idle. TBD: Ideally we can change the return value
* to something like __thread_has_fpu(current). But we need to
* be careful of doing __thread_clear_has_fpu() before saving
* the FPU etc for supporting nested uses etc. For now, take
@@ -38,7 +37,7 @@
*/
static inline bool interrupted_kernel_fpu_idle(void)
{
- if (use_xsave())
+ if (use_eager_fpu())
return 0;

return !__thread_has_fpu(current) &&
@@ -84,7 +83,7 @@ void kernel_fpu_begin(void)
__save_init_fpu(me);
__thread_clear_has_fpu(me);
/* We do 'stts()' in kernel_fpu_end() */
- } else if (!use_xsave()) {
+ } else if (!use_eager_fpu()) {
this_cpu_write(fpu_owner_task, NULL);
clts();
}
@@ -93,7 +92,7 @@ EXPORT_SYMBOL(kernel_fpu_begin);

void kernel_fpu_end(void)
{
- if (use_xsave())
+ if (use_eager_fpu())
math_state_restore();
else
stts();
@@ -122,7 +121,6 @@ static void __cpuinit mxcsr_feature_mask_init(void)
{
unsigned long mask = 0;

- clts();
if (cpu_has_fxsr) {
memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
asm volatile("fxsave %0" : : "m" (fx_scratch));
@@ -131,7 +129,6 @@ static void __cpuinit mxcsr_feature_mask_init(void)
mask = 0x0000ffbf;
}
mxcsr_feature_mask &= mask;
- stts();
}

static void __cpuinit init_thread_xstate(void)
@@ -185,9 +182,8 @@ void __cpuinit fpu_init(void)
init_thread_xstate();

mxcsr_feature_mask_init();
- /* clean state in init */
- current_thread_info()->status = 0;
- clear_used_math();
+ xsave_init();
+ eager_fpu_init();
}

void fpu_finit(struct fpu *fpu)
@@ -198,12 +194,7 @@ void fpu_finit(struct fpu *fpu)
}

if (cpu_has_fxsr) {
- struct i387_fxsave_struct *fx = &fpu->state->fxsave;
-
- memset(fx, 0, xstate_size);
- fx->cwd = 0x37f;
- if (cpu_has_xmm)
- fx->mxcsr = MXCSR_DEFAULT;
+ fx_finit(&fpu->state->fxsave);
} else {
struct i387_fsave_struct *fp = &fpu->state->fsave;
memset(fp, 0, xstate_size);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c21e30f..dc3567e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -156,7 +156,7 @@ void flush_thread(void)
* Free the FPU state for non xsave platforms. They get reallocated
* lazily at the first use.
*/
- if (!use_xsave())
+ if (!use_eager_fpu())
free_thread_xstate(tsk);
}

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ac7d527..4f4aba0 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -630,7 +630,7 @@ EXPORT_SYMBOL_GPL(math_state_restore);
dotraplinkage void __kprobes
do_device_not_available(struct pt_regs *regs, long error_code)
{
- BUG_ON(use_xsave());
+ BUG_ON(use_eager_fpu());

#ifdef CONFIG_MATH_EMULATION
if (read_cr0() & X86_CR0_EM) {
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 55bf571..66369f4 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -399,7 +399,7 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
set_used_math();
}

- if (use_xsave())
+ if (use_eager_fpu())
math_state_restore();

return err;
@@ -449,29 +449,11 @@ static void prepare_fx_sw_frame(void)
*/
static inline void xstate_enable(void)
{
- clts();
set_in_cr4(X86_CR4_OSXSAVE);
xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
}

/*
- * This is same as math_state_restore(). But use_xsave() is not yet
- * patched to use math_state_restore().
- */
-static inline void init_restore_xstate(void)
-{
- init_fpu(current);
- __thread_fpu_begin(current);
- xrstor_state(init_xstate_buf, -1);
-}
-
-static inline void xstate_enable_ap(void)
-{
- xstate_enable();
- init_restore_xstate();
-}
-
-/*
* Record the offsets and sizes of different state managed by the xsave
* memory layout.
*/
@@ -499,17 +481,20 @@ static void __init setup_xstate_features(void)
/*
* setup the xstate image representing the init state
*/
-static void __init setup_xstate_init(void)
+static void __init setup_init_fpu_buf(void)
{
- setup_xstate_features();
-
/*
* Setup init_xstate_buf to represent the init state of
* all the features managed by the xsave
*/
init_xstate_buf = alloc_bootmem_align(xstate_size,
__alignof__(struct xsave_struct));
- init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
+ fx_finit(&init_xstate_buf->i387);
+
+ if (!cpu_has_xsave)
+ return;
+
+ setup_xstate_features();

/*
* Init all the features state with header_bv being 0x0
@@ -522,6 +507,17 @@ static void __init setup_xstate_init(void)
xsave_state(init_xstate_buf, -1);
}

+static int disable_eagerfpu;
+static int __init eager_fpu_setup(char *s)
+{
+ if (!strcmp(s, "on"))
+ setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
+ else if (!strcmp(s, "off"))
+ disable_eagerfpu = 1;
+ return 1;
+}
+__setup("eagerfpu=", eager_fpu_setup);
+
/*
* Enable and initialize the xsave feature.
*/
@@ -558,15 +554,10 @@ static void __init xstate_enable_boot_cpu(void)

update_regset_xstate_info(xstate_size, pcntxt_mask);
prepare_fx_sw_frame();
-
- setup_xstate_init();
+ setup_init_fpu_buf();

pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
pcntxt_mask, xstate_size);
-
- current->thread.fpu.state =
- alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
- init_restore_xstate();
}

/*
@@ -585,6 +576,42 @@ void __cpuinit xsave_init(void)
return;

this_func = next_func;
- next_func = xstate_enable_ap;
+ next_func = xstate_enable;
this_func();
}
+
+static inline void __init eager_fpu_init_bp(void)
+{
+ current->thread.fpu.state =
+ alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
+ if (!init_xstate_buf)
+ setup_init_fpu_buf();
+}
+
+void __cpuinit eager_fpu_init(void)
+{
+ static __refdata void (*boot_func)(void) = eager_fpu_init_bp;
+
+ clear_used_math();
+ current_thread_info()->status = 0;
+ if (!cpu_has_eager_fpu) {
+ stts();
+ return;
+ }
+
+ if (boot_func) {
+ boot_func();
+ boot_func = NULL;
+ }
+
+ /*
+ * This is same as math_state_restore(). But use_xsave() is
+ * not yet patched to use math_state_restore().
+ */
+ init_fpu(current);
+ __thread_fpu_begin(current);
+ if (cpu_has_xsave)
+ xrstor_state(init_xstate_buf, -1);
+ else
+ fxrstor_checking(&init_xstate_buf->i387);
+}
--
1.7.6.5


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