module: freebsd: fix aarch64 fpu handling

Just like x86, aarch64 needs to use the fpu_kern(9) API around FPU
usage, otherwise we panic promptly at boot as soon as ZFS attempts to
do checksum benchmarking.

Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Closes #14715

Author: kevans91

include/os/freebsd/spl/sys/simd_aarch64.h

@@ -44,13 +44,23 @@
 #define	_FREEBSD_SIMD_AARCH64_H
 
 #include <sys/types.h>
+#include <sys/ucontext.h>
 #include <machine/elf.h>
+#include <machine/fpu.h>
 #include <machine/md_var.h>
+#include <machine/pcb.h>
 
 #define	kfpu_allowed()		1
 #define	kfpu_initialize(tsk)	do {} while (0)
-#define	kfpu_begin()		do {} while (0)
-#define	kfpu_end()		do {} while (0)
+#define	kfpu_begin() do {						\
+	if (__predict_false(!is_fpu_kern_thread(0)))			\
+		fpu_kern_enter(curthread, NULL, FPU_KERN_NOCTX);	\
+} while (0)
+
+#define	kfpu_end() do {							\
+	if (__predict_false(curthread->td_pcb->pcb_fpflags & PCB_FP_NOSAVE)) \
+		fpu_kern_leave(curthread, NULL);			\
+} while (0)
 #define	kfpu_init()		(0)
 #define	kfpu_fini()		do {} while (0)