Add cpu_sync_core()

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D32360

sys/amd64/amd64/support.S

@@ -1969,3 +1969,24 @@ ENTRY(mds_handler_silvermont)
 	popq	%rax
 	retq
 END(mds_handler_silvermont)
+
+/*
+ * Do the same as Linux and execute IRET explicitly, despite IPI
+ * return does it as well.
+ */
+ENTRY(cpu_sync_core)
+/*
+ * Can utilize SERIALIZE when instruction is moved from
+ * 'future extensions' to SDM.
+ */
+	movq	(%rsp), %rdx
+	movl	%ss, %eax
+	pushq	%rax
+	pushq	%rsp
+	addq	$16, (%rsp)
+	pushfq
+	movl	%cs, %eax
+	pushq	%rax
+	pushq	%rdx
+	iretq
+END(cpu_sync_core)

sys/arm/arm/vm_machdep.c

@@ -311,3 +311,8 @@ cpu_procctl(struct thread *td __unused, int idtype __unused, id_t id __unused,
 
 	return (EINVAL);
 }
+
+void
+cpu_sync_core(void)
+{
+}

sys/arm64/arm64/vm_machdep.c

@@ -310,3 +310,14 @@ cpu_procctl(struct thread *td __unused, int idtype __unused, id_t id __unused,
 
 	return (EINVAL);
 }
+
+void
+cpu_sync_core(void)
+{
+	/*
+	 * Do nothing. According to ARM ARMv8 D1.11 Exception return
+	 * If FEAT_ExS is not implemented, or if FEAT_ExS is
+	 * implemented and the SCTLR_ELx.EOS field is set, exception
+	 * return from ELx is a context synchronization event.
+	 */
+}

sys/i386/i386/support.S

@@ -578,3 +578,11 @@ ENTRY(mds_handler_silvermont)
 	movl	%eax, %cr0
 3:	ret
 END(mds_handler_silvermont)
+
+ENTRY(cpu_sync_core)
+	popl	%eax
+	pushfl
+	pushl	%cs
+	pushl	%eax
+	iretl
+END(cpu_sync_core)

sys/powerpc/powerpc/vm_machdep.c

@@ -239,3 +239,13 @@ cpu_procctl(struct thread *td __unused, int idtype __unused, id_t id __unused,
 
 	return (EINVAL);
 }
+
+void
+cpu_sync_core(void)
+{
+	/*
+	 * Linux performs "rfi" there.  Our rendezvous IPI handler on
+	 * the target cpu does "rfi" before and lwsync/sync after the
+	 * action, which is stronger than required.
+	 */
+}

sys/riscv/riscv/vm_machdep.c

@@ -49,6 +49,7 @@
 
 #include <machine/riscvreg.h>
 #include <machine/cpu.h>
+#include <machine/cpufunc.h>
 #include <machine/pcb.h>
 #include <machine/frame.h>
 #include <machine/sbi.h>
@@ -267,3 +268,9 @@ cpu_procctl(struct thread *td __unused, int idtype __unused, id_t id __unused,
 
 	return (EINVAL);
 }
+
+void
+cpu_sync_core(void)
+{
+	fence_i();
+}

sys/sys/proc.h

@@ -1229,6 +1229,7 @@ void	cpu_idle(int);
 int	cpu_idle_wakeup(int);
 extern	void (*cpu_idle_hook)(sbintime_t);	/* Hook to machdep CPU idler. */
 void	cpu_switch(struct thread *, struct thread *, struct mtx *);
+void	cpu_sync_core(void);
 void	cpu_throw(struct thread *, struct thread *) __dead2;
 bool	curproc_sigkilled(void);
 void	userret(struct thread *, struct trapframe *);