Reduce an arm64 VFP critical section

In set_fpcontext we only need a critical section around vfp_discard.
The remainder of the code can run without it.

While here add an assert to check the passed in thread is the
current thread as the code already this.

Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D38000

1 files changed, 3 insertions, 4 deletions

diff --git a/sys/arm64/arm64/exec_machdep.c b/sys/arm64/arm64/exec_machdep.c
index 258cb5d26b13..27ee2f80858d 100644
--- a/sys/arm64/arm64/exec_machdep.c
+++ b/sys/arm64/arm64/exec_machdep.c
@@ -519,8 +519,7 @@ set_fpcontext(struct thread *td, mcontext_t *mcp)
 #ifdef VFP
 	struct pcb *curpcb;
 
-	critical_enter();
-
+	MPASS(td == curthread);
 	if ((mcp->mc_flags & _MC_FP_VALID) != 0) {
 		curpcb = curthread->td_pcb;
 
@@ -528,7 +527,9 @@ set_fpcontext(struct thread *td, mcontext_t *mcp)
 		 * Discard any vfp state for the current thread, we
 		 * are about to override it.
 		 */
+		critical_enter();
 		vfp_discard(td);
+		critical_exit();
 
 		KASSERT(curpcb->pcb_fpusaved == &curpcb->pcb_fpustate,
 		    ("Called set_fpcontext while the kernel is using the VFP"));
@@ -538,8 +539,6 @@ set_fpcontext(struct thread *td, mcontext_t *mcp)
 		curpcb->pcb_fpustate.vfp_fpsr = mcp->mc_fpregs.fp_sr;
 		curpcb->pcb_fpflags = mcp->mc_fpregs.fp_flags & PCB_FP_USERMASK;
 	}
-
-	critical_exit();
 #endif
 }