linux-kernel - [PATCH 7/9] x86/fpu: rename lazy restore functions to "register state valid"

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Date:   Tue,  4 Oct 2016 20:34:36 -0400
From:   riel@...hat.com
To:     linux-kernel@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com, x86@...nel.org, tglx@...utronix.de,
        pbonzini@...hat.com, mingo@...hat.com, luto@...nel.org,
        pa@...or.com, bp@...e.de
Subject: [PATCH 7/9] x86/fpu: rename lazy restore functions to "register state valid"

From: Rik van Riel <riel@...hat.com>

Name the functions after the state they track, rather than the function
they currently enable. This should make it more obvious when we use the
fpu_register_state_valid function for something else in the future.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 arch/x86/include/asm/fpu/internal.h | 26 ++++++++++++++++++++------
 arch/x86/kernel/fpu/core.c          |  4 ++--
 arch/x86/kernel/smpboot.c           |  2 +-
 3 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 499d6ed0e376..d2cfe16dd9fa 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -479,18 +479,32 @@ extern int copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size)
 DECLARE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
 /*
+ * The in-register FPU state for an FPU context on a CPU is assumed to be
+ * valid if the fpu->last_cpu matches the CPU, and the fpu_fpregs_owner_ctx
+ * matches the FPU.
+ *
+ * If the FPU register state is valid, the kernel can skip restoring the
+ * FPU state from memory.
+ *
+ * Any code that clobbers the FPU registers or updates the in-memory
+ * FPU state for a task MUST let the rest of the kernel know that the
+ * FPU registers are no longer valid for this task. Calling either of
+ * these two invalidate functions is enough, use whichever is convenient.
+ *
  * Must be run with preemption disabled: this clears the fpu_fpregs_owner_ctx,
  * on this CPU.
- *
- * This will disable any lazy FPU state restore of the current FPU state,
- * but if the current thread owns the FPU, it will still be saved by.
  */
-static inline void __cpu_disable_lazy_restore(unsigned int cpu)
+static inline void __cpu_invalidate_fpregs_state(unsigned int cpu)
 {
 	per_cpu(fpu_fpregs_owner_ctx, cpu) = NULL;
 }
 
-static inline int fpu_want_lazy_restore(struct fpu *fpu, unsigned int cpu)
+static inline void __fpu_invalidate_fpregs_state(struct fpu *fpu)
+{
+	fpu->last_cpu = -1;
+}
+
+static inline int fpregs_state_valid(struct fpu *fpu, unsigned int cpu)
 {
 	return fpu == this_cpu_read_stable(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
 }
@@ -588,7 +602,7 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu)
 	} else {
 		old_fpu->last_cpu = -1;
 		if (fpu.preload) {
-			if (fpu_want_lazy_restore(new_fpu, cpu))
+			if (fpregs_state_valid(new_fpu, cpu))
 				fpu.preload = 0;
 			else
 				prefetch(&new_fpu->state);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 6a37d525bdbe..25a45ddfdbcf 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -336,7 +336,7 @@ void fpu__activate_fpstate_write(struct fpu *fpu)
 
 	if (fpu->fpstate_active) {
 		/* Invalidate any lazy state: */
-		fpu->last_cpu = -1;
+		__fpu_invalidate_fpregs_state(fpu);
 	} else {
 		fpstate_init(&fpu->state);
 		trace_x86_fpu_init_state(fpu);
@@ -379,7 +379,7 @@ void fpu__current_fpstate_write_begin(void)
 	 * ensures we will not be lazy and skip a XRSTOR in the
 	 * future.
 	 */
-	fpu->last_cpu = -1;
+	__fpu_invalidate_fpregs_state(fpu);
 }
 
 /*
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 42a93621f5b0..ca4c4ca2f6af 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1111,7 +1111,7 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 		return err;
 
 	/* the FPU context is blank, nobody can own it */
-	__cpu_disable_lazy_restore(cpu);
+	__cpu_invalidate_fpregs_state(cpu);
 
 	common_cpu_up(cpu, tidle);
 
-- 
2.7.4