Revert "ARM: vfp: fix a hole in VFP thread migration"

This reverts commit c0822d4f0bcccf227b751cfe1c047f3bdae0f1ce.

2 files changed, 55 insertions, 86 deletions

diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index 2d30c7f6edd3..404538ae591d 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -82,22 +82,19 @@ ENTRY(vfp_support_entry)
 	ldr	r4, [r3, r11, lsl #2]	@ vfp_current_hw_state pointer
 	bic	r5, r1, #FPEXC_EX	@ make sure exceptions are disabled
 	cmp	r4, r10			@ this thread owns the hw context?
-#ifndef CONFIG_SMP
-	@ For UP, checking that this thread owns the hw context is
-	@ sufficient to determine that the hardware state is valid.
 	beq	vfp_hw_state_valid
 
-	@ On UP, we lazily save the VFP context.  As a different
-	@ thread wants ownership of the VFP hardware, save the old
-	@ state if there was a previous (valid) owner.
-
 	VFPFMXR	FPEXC, r5		@ enable VFP, disable any pending
 					@ exceptions, so we can get at the
 					@ rest of it
 
+#ifndef CONFIG_SMP
+	@ Save out the current registers to the old thread state
+	@ No need for SMP since this is not done lazily
+
 	DBGSTR1	"save old state %p", r4
-	cmp	r4, #0			@ if the vfp_current_hw_state is NULL
-	beq	vfp_reload_hw		@ then the hw state needs reloading
+	cmp	r4, #0
+	beq	no_old_VFP_process
 	VFPFSTMIA r4, r5		@ save the working registers
 	VFPFMRX	r5, FPSCR		@ current status
 #ifndef CONFIG_CPU_FEROCEON
@@ -110,33 +107,11 @@ ENTRY(vfp_support_entry)
 1:
 #endif
 	stmia	r4, {r1, r5, r6, r8}	@ save FPEXC, FPSCR, FPINST, FPINST2
-vfp_reload_hw:
-
-#else
-	@ For SMP, if this thread does not own the hw context, then we
-	@ need to reload it.  No need to save the old state as on SMP,
-	@ we always save the state when we switch away from a thread.
-	bne	vfp_reload_hw
-
-	@ This thread has ownership of the current hardware context.
-	@ However, it may have been migrated to another CPU, in which
-	@ case the saved state is newer than the hardware context.
-	@ Check this by looking at the CPU number which the state was
-	@ last loaded onto.
-	ldr	ip, [r10, #VFP_CPU]
-	teq	ip, r11
-	beq	vfp_hw_state_valid
-
-vfp_reload_hw:
-	@ We're loading this threads state into the VFP hardware. Update
-	@ the CPU number which contains the most up to date VFP context.
-	str	r11, [r10, #VFP_CPU]
-
-	VFPFMXR	FPEXC, r5		@ enable VFP, disable any pending
-					@ exceptions, so we can get at the
-					@ rest of it
+					@ and point r4 at the word at the
+					@ start of the register dump
 #endif
 
+no_old_VFP_process:
 	DBGSTR1	"load state %p", r10
 	str	r10, [r3, r11, lsl #2]	@ update the vfp_current_hw_state pointer
 					@ Load the saved state back into the VFP
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index daa69a271acc..871f03c90b34 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -35,51 +35,18 @@ void vfp_null_entry(void);
 void (*vfp_vector)(void) = vfp_null_entry;
 
 /*
- * Dual-use variable.
- * Used in startup: set to non-zero if VFP checks fail
- * After startup, holds VFP architecture
- */
-unsigned int VFP_arch;
-
-/*
  * The pointer to the vfpstate structure of the thread which currently
  * owns the context held in the VFP hardware, or NULL if the hardware
  * context is invalid.
- *
- * For UP, this is sufficient to tell which thread owns the VFP context.
- * However, for SMP, we also need to check the CPU number stored in the
- * saved state too to catch migrations.
  */
 union vfp_state *vfp_current_hw_state[NR_CPUS];
 
 /*
- * Is 'thread's most up to date state stored in this CPUs hardware?
- * Must be called from non-preemptible context.
- */
-static bool vfp_state_in_hw(unsigned int cpu, struct thread_info *thread)
-{
-#ifdef CONFIG_SMP
-	if (thread->vfpstate.hard.cpu != cpu)
-		return false;
-#endif
-	return vfp_current_hw_state[cpu] == &thread->vfpstate;
-}
-
-/*
- * Force a reload of the VFP context from the thread structure.  We do
- * this by ensuring that access to the VFP hardware is disabled, and
- * clear last_VFP_context.  Must be called from non-preemptible context.
+ * Dual-use variable.
+ * Used in startup: set to non-zero if VFP checks fail
+ * After startup, holds VFP architecture
  */
-static void vfp_force_reload(unsigned int cpu, struct thread_info *thread)
-{
-	if (vfp_state_in_hw(cpu, thread)) {
-		fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
-		vfp_current_hw_state[cpu] = NULL;
-	}
-#ifdef CONFIG_SMP
-	thread->vfpstate.hard.cpu = NR_CPUS;
-#endif
-}
+unsigned int VFP_arch;
 
 /*
  * Per-thread VFP initialization.
@@ -93,9 +60,6 @@ static void vfp_thread_flush(struct thread_info *thread)
 
 	vfp->hard.fpexc = FPEXC_EN;
 	vfp->hard.fpscr = FPSCR_ROUND_NEAREST;
-#ifdef CONFIG_SMP
-	vfp->hard.cpu = NR_CPUS;
-#endif
 
 	/*
 	 * Disable VFP to ensure we initialize it first.  We must ensure
@@ -126,9 +90,6 @@ static void vfp_thread_copy(struct thread_info *thread)
 
 	vfp_sync_hwstate(parent);
 	thread->vfpstate = parent->vfpstate;
-#ifdef CONFIG_SMP
-	thread->vfpstate.hard.cpu = NR_CPUS;
-#endif
 }
 
 /*
@@ -174,8 +135,17 @@ static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
 		 * case the thread migrates to a different CPU. The
 		 * restoring is done lazily.
 		 */
-		if ((fpexc & FPEXC_EN) && vfp_current_hw_state[cpu])
+		if ((fpexc & FPEXC_EN) && vfp_current_hw_state[cpu]) {
 			vfp_save_state(vfp_current_hw_state[cpu], fpexc);
+			vfp_current_hw_state[cpu]->hard.cpu = cpu;
+		}
+		/*
+		 * Thread migration, just force the reloading of the
+		 * state on the new CPU in case the VFP registers
+		 * contain stale data.
+		 */
+		if (thread->vfpstate.hard.cpu != cpu)
+			vfp_current_hw_state[cpu] = NULL;
 #endif
 
 		/*
@@ -483,15 +453,15 @@ static void vfp_pm_init(void)
 static inline void vfp_pm_init(void) { }
 #endif /* CONFIG_PM */
 
-/*
- * Ensure that the VFP state stored in 'thread->vfpstate' is up to date
- * with the hardware state.
- */
 void vfp_sync_hwstate(struct thread_info *thread)
 {
 	unsigned int cpu = get_cpu();
 
-	if (vfp_state_in_hw(cpu, thread)) {
+	/*
+	 * If the thread we're interested in is the current owner of the
+	 * hardware VFP state, then we need to save its state.
+	 */
+	if (vfp_current_hw_state[cpu] == &thread->vfpstate) {
 		u32 fpexc = fmrx(FPEXC);
 
 		/*
@@ -505,13 +475,36 @@ void vfp_sync_hwstate(struct thread_info *thread)
 	put_cpu();
 }
 
-/* Ensure that the thread reloads the hardware VFP state on the next use. */
 void vfp_flush_hwstate(struct thread_info *thread)
 {
 	unsigned int cpu = get_cpu();
 
-	vfp_force_reload(cpu, thread);
+	/*
+	 * If the thread we're interested in is the current owner of the
+	 * hardware VFP state, then we need to save its state.
+	 */
+	if (vfp_current_hw_state[cpu] == &thread->vfpstate) {
+		u32 fpexc = fmrx(FPEXC);
 
+		fmxr(FPEXC, fpexc & ~FPEXC_EN);
+
+		/*
+		 * Set the context to NULL to force a reload the next time
+		 * the thread uses the VFP.
+		 */
+		vfp_current_hw_state[cpu] = NULL;
+	}
+
+#ifdef CONFIG_SMP
+	/*
+	 * For SMP we still have to take care of the case where the thread
+	 * migrates to another CPU and then back to the original CPU on which
+	 * the last VFP user is still the same thread. Mark the thread VFP
+	 * state as belonging to a non-existent CPU so that the saved one will
+	 * be reloaded in the above case.
+	 */
+	thread->vfpstate.hard.cpu = NR_CPUS;
+#endif
 	put_cpu();
 }
 
@@ -530,7 +523,8 @@ static int vfp_hotplug(struct notifier_block *b, unsigned long action,
 	void *hcpu)
 {
 	if (action == CPU_DYING || action == CPU_DYING_FROZEN) {
-		vfp_force_reload((long)hcpu, current_thread_info());
+		unsigned int cpu = (long)hcpu;
+		vfp_current_hw_state[cpu] = NULL;
 	} else if (action == CPU_STARTING || action == CPU_STARTING_FROZEN)
 		vfp_enable(NULL);
 	return NOTIFY_OK;