[RFC PATCH 0.9/2] arm64: fpsimd: Expose CPU / FPSIMD state association helpers

[Dave Martin]

Oops, forgot to post this patch that goes before patch 1 in the series.

--8<--

Expose an interface for associating an FPSIMD context with a CPU and
checking the association, for use by KVM.

Signed-off-by: Dave Martin <Dave.Martin at arm.com>
---
 arch/arm64/include/asm/fpsimd.h |  5 +++++
 arch/arm64/kernel/fpsimd.c      | 42 +++++++++++++++++++++++++++++------------
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index 8857a0f..f4ce4d6 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -23,6 +23,7 @@
 
 #include <linux/cache.h>
 #include <linux/stddef.h>
+#include <linux/types.h>
 
 /*
  * FP/SIMD storage area has:
@@ -62,6 +63,8 @@ struct fpsimd_state {
 
 struct task_struct;
 
+extern bool fpsimd_foreign_fpstate(struct fpsimd_state const *state);
+
 extern void fpsimd_save_state(struct fpsimd_state *state);
 extern void fpsimd_load_state(struct fpsimd_state *state);
 
@@ -76,6 +79,8 @@ extern void fpsimd_update_current_state(struct user_fpsimd_state const *state);
 extern void fpsimd_flush_task_state(struct task_struct *target);
 extern void sve_flush_cpu_state(void);
 
+extern void fpsimd_bind_state_to_cpu(struct fpsimd_state *state);
+
 /* Maximum VL that SVE VL-agnostic software can transparently support */
 #define SVE_VL_ARCH_MAX 0x100
 
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e7226c4..138efaf 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -38,6 +38,7 @@
 #include <linux/signal.h>
 #include <linux/slab.h>
 #include <linux/sysctl.h>
+#include <linux/types.h>
 
 #include <asm/fpsimd.h>
 #include <asm/cputype.h>
@@ -121,6 +122,14 @@ struct fpsimd_last_state_struct {
 
 static DEFINE_PER_CPU(struct fpsimd_last_state_struct, fpsimd_last_state);
 
+bool fpsimd_foreign_fpstate(struct fpsimd_state const *st)
+{
+	WARN_ON(!in_softirq() && !irqs_disabled());
+
+	return st->cpu != smp_processor_id() ||
+		st != __this_cpu_read(fpsimd_last_state.st);
+}
+
 /* Default VL for tasks that don't set it explicitly: */
 static int sve_default_vl = -1;
 
@@ -908,13 +917,10 @@ void fpsimd_thread_switch(struct task_struct *next)
 		 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
 		 * upon the next return to userland.
 		 */
-		struct fpsimd_state *st = &next->thread.fpsimd_state;
-
-		if (__this_cpu_read(fpsimd_last_state.st) == st
-		    && st->cpu == smp_processor_id())
-			clear_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
-		else
+		if (fpsimd_foreign_fpstate(&current->thread.fpsimd_state))
 			set_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
+		else
+			clear_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
 	}
 }
 
@@ -996,19 +1002,31 @@ void fpsimd_signal_preserve_current_state(void)
 		sve_to_fpsimd(current);
 }
 
+static void __fpsimd_bind_to_cpu(struct fpsimd_last_state_struct *last,
+				 struct fpsimd_state *st)
+{
+	WARN_ON(!in_softirq() || !irqs_disabled());
+
+	last->st = st;
+	st->cpu = smp_processor_id();
+}
+
+void fpsimd_bind_state_to_cpu(struct fpsimd_state *st)
+{
+	__fpsimd_bind_to_cpu(this_cpu_ptr(&fpsimd_last_state), st);
+}
+
 /*
  * Associate current's FPSIMD context with this cpu
  * Preemption must be disabled when calling this function.
  */
-static void fpsimd_bind_to_cpu(void)
+static void fpsimd_bind_task_to_cpu(void)
 {
 	struct fpsimd_last_state_struct *last =
 		this_cpu_ptr(&fpsimd_last_state);
-	struct fpsimd_state *st = &current->thread.fpsimd_state;
 
-	last->st = st;
+	__fpsimd_bind_to_cpu(last, &current->thread.fpsimd_state);
 	last->sve_in_use = test_thread_flag(TIF_SVE);
-	st->cpu = smp_processor_id();
 }
 
 /*
@@ -1025,7 +1043,7 @@ void fpsimd_restore_current_state(void)
 
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
 		task_fpsimd_load();
-		fpsimd_bind_to_cpu();
+		fpsimd_bind_task_to_cpu();
 	}
 
 	local_bh_enable();
@@ -1050,7 +1068,7 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state)
 	task_fpsimd_load();
 
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE))
-		fpsimd_bind_to_cpu();
+		fpsimd_bind_task_to_cpu();
 
 	local_bh_enable();
 }
-- 
2.1.4