[RFC PATCH 3/6] prctl: Define PowerPC DEXCR interface

[Benjamin Gray <bgray@linux.ibm.com>]

Adds the definitions and generic handler for prctl control of the
PowerPC Dynamic Execution Control Register (DEXCR).

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
 include/uapi/linux/prctl.h | 13 +++++++++++++
 kernel/sys.c               | 16 ++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 3c36aeade991..85d66ad134b1 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -305,4 +305,17 @@ struct prctl_mm_map {
 # define PR_RISCV_V_VSTATE_CTRL_NEXT_MASK	0xc
 # define PR_RISCV_V_VSTATE_CTRL_MASK		0x1f
 
+/* PowerPC Dynamic Execution Control Register (DEXCR) controls */
+#define PR_PPC_GET_DEXCR		71
+#define PR_PPC_SET_DEXCR		72
+/* DEXCR aspect to act on */
+# define PR_PPC_DEXCR_SBHE		0 /* Speculative branch hint enable */
+# define PR_PPC_DEXCR_IBRTPD		1 /* Indirect branch recurrent target prediction disable */
+# define PR_PPC_DEXCR_SRAPD		2 /* Subroutine return address prediction disable */
+# define PR_PPC_DEXCR_NPHIE		3 /* Non-privileged hash instruction enable */
+/* Action to apply / return */
+# define PR_PPC_DEXCR_CTRL_OFF		(1UL << 0)
+# define PR_PPC_DEXCR_CTRL_ON		(1UL << 1)
+# define PR_PPC_DEXCR_CTRL_INHERIT	(1UL << 2)
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 2410e3999ebe..0c1b8e9c3d16 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -146,6 +146,12 @@
 #ifndef RISCV_V_GET_CONTROL
 # define RISCV_V_GET_CONTROL()		(-EINVAL)
 #endif
+#ifndef PPC_GET_DEXCR_ASPECT
+# define PPC_GET_DEXCR_ASPECT(a, b)	(-EINVAL)
+#endif
+#ifndef PPC_SET_DEXCR_ASPECT
+# define PPC_SET_DEXCR_ASPECT(a, b, c)	(-EINVAL)
+#endif
 
 /*
  * this is where the system-wide overflow UID and GID are defined, for
@@ -2686,6 +2692,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 	case PR_GET_MDWE:
 		error = prctl_get_mdwe(arg2, arg3, arg4, arg5);
 		break;
+	case PR_PPC_GET_DEXCR:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = PPC_GET_DEXCR_ASPECT(me, arg2);
+		break;
+	case PR_PPC_SET_DEXCR:
+		if (arg4 || arg5)
+			return -EINVAL;
+		error = PPC_SET_DEXCR_ASPECT(me, arg2, arg3);
+		break;
 	case PR_SET_VMA:
 		error = prctl_set_vma(arg2, arg3, arg4, arg5);
 		break;
-- 
2.41.0