x86, fpu: decouple non-lazy/eager fpu restore from xsave

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>
Link: http://lkml.kernel.org/r/1347300665-6209-2-git-send-email-suresh.b.siddha@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

8 files changed, 112 insertions, 66 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index ad7e2e5088c1..741d064fdc6a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1833,6 +1833,10 @@ 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 6b7ee5ff6820..5dd2b473ccff 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 */
@@ -305,6 +306,7 @@ 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 8ca0f9f45ac4..0ca72f0d4b41 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 a5fbc3c5fccc..b0fe078614d8 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1297,7 +1297,6 @@ void __cpuinit cpu_init(void)
         dbg_restore_debug_regs();
 
         fpu_init();
-        xsave_init();
 
         raw_local_save_flags(kernel_eflags);
 
@@ -1352,6 +1351,5 @@ 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 528557470ddb..6782e3983865 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 c21e30f8923b..dc3567e083f9 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 ac7d5275f6e8..4f4aba0551b0 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 e7752bd7cac8..c0afd2c43761 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -400,7 +400,7 @@ 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;
@@ -450,29 +450,11 @@ 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.
  */
@@ -500,17 +482,20 @@ 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
@@ -523,6 +508,17 @@ 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.
  */
@@ -559,15 +555,10 @@ 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();
 }
 
 /*
@@ -586,6 +577,42 @@ 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);
+}