Update some comments related to use of amd64 full context switch.

In exec_linux_setregs(), use locally cached pointer to pcb to set
pcb_full_iret.
In set_regs(), note that full return is needed when code that sets
segment registers is enabled.

MFC after:	1 week

3 files changed, 5 insertions, 5 deletions

diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index d09ae4a..fe4deb7 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -1906,6 +1906,7 @@ set_regs(struct thread *td, struct reg *regs)
 		tp->tf_fs = regs->r_fs;
 		tp->tf_gs = regs->r_gs;
 		tp->tf_flags = TF_HASSEGS;
+		td->td_pcb->pcb_full_iret = 1;
 	}
 	return (0);
 }
diff --git a/sys/amd64/amd64/vm_machdep.c b/sys/amd64/amd64/vm_machdep.c
index 2a93bc1..b966393 100644
--- a/sys/amd64/amd64/vm_machdep.c
+++ b/sys/amd64/amd64/vm_machdep.c
@@ -339,10 +339,9 @@ cpu_set_syscall_retval(struct thread *td, int error)
 		 * Reconstruct pc, we know that 'syscall' is 2 bytes,
 		 * lcall $X,y is 7 bytes, int 0x80 is 2 bytes.
 		 * We saved this in tf_err.
-		 * We have to do a full context restore so that %r10
-		 * (which was holding the value of %rcx) is restored
+		 * %r10 (which was holding the value of %rcx) is restored
 		 * for the next iteration.
-		 * r10 restore is only required for freebsd/amd64 processes,
+		 * %r10 restore is only required for freebsd/amd64 processes,
 		 * but shall be innocent for any ia32 ABI.
 		 */
 		td->td_frame->tf_rip -= td->td_frame->tf_err;
diff --git a/sys/amd64/linux32/linux32_sysvec.c b/sys/amd64/linux32/linux32_sysvec.c
index 0dbcef4..3ebb980 100644
--- a/sys/amd64/linux32/linux32_sysvec.c
+++ b/sys/amd64/linux32/linux32_sysvec.c
@@ -865,13 +865,13 @@ exec_linux_setregs(struct thread *td, struct image_params *imgp, u_long stack)
 	regs->tf_flags = TF_HASSEGS;
 	regs->tf_cs = _ucode32sel;
 	regs->tf_rbx = imgp->ps_strings;
-	td->td_pcb->pcb_full_iret = 1;
 	load_cr0(rcr0() | CR0_MP | CR0_TS);
 	fpstate_drop(td);
 
-	/* Return via doreti so that we can change to a different %cs */
+	/* Do full restore on return so that we can change to a different %cs */
 	pcb->pcb_flags |= PCB_32BIT;
 	pcb->pcb_flags &= ~PCB_GS32BIT;
+	pcb->pcb_full_iret = 1;
 	td->td_retval[1] = 0;
 }