Subject: [RFC PATCH 05/13] prctl: Define PowerPC DEXCR interface

From: Benjamin Gray <[email-masked]>
Date: Mon, 28 Nov 2022 13:44:50 +1100

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

Signed-off-by: Benjamin Gray <[email-masked]>
---
 include/uapi/linux/prctl.h | 14 ++++++++++++++
 kernel/sys.c               | 16 ++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index a5e06dcbba13..b4720e8de6f3 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -281,6 +281,20 @@ struct prctl_mm_map {
 # define PR_SME_VL_LEN_MASK		0xffff
 # define PR_SME_VL_INHERIT		(1 << 17) /* inherit across exec */
 
+/* PowerPC Dynamic Execution Control Register (DEXCR) controls */
+#define PR_PPC_GET_DEXCR		65
+#define PR_PPC_SET_DEXCR		66
+/* 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_PRCTL		(1 << 0)
+# define PR_PPC_DEXCR_SET_ASPECT	(1 << 1)
+# define PR_PPC_DEXCR_FORCE_SET_ASPECT	(1 << 2)
+# define PR_PPC_DEXCR_CLEAR_ASPECT	(1 << 3)
+
 #define PR_SET_VMA		0x53564d41
 # define PR_SET_VMA_ANON_NAME		0
 
diff --git a/kernel/sys.c b/kernel/sys.c
index 5fd54bf0e886..55b8f7369059 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -139,6 +139,12 @@
 #ifndef GET_TAGGED_ADDR_CTRL
 # define GET_TAGGED_ADDR_CTRL()		(-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
@@ -2623,6 +2629,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		error = sched_core_share_pid(arg2, arg3, arg4, arg5);
 		break;
 #endif
+	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;
-- 
2.38.1