Workaround for Linux PowerPC GPL-only cpu_has_feature()

Linux since 4.7 makes interface 'cpu_has_feature' to use jump labels on
powerpc if CONFIG_JUMP_LABEL_FEATURE_CHECKS is enabled, in this case however
this inline function references GPL-only symbol 'cpu_feature_keys'.

ZFS currently uses 'cpu_has_feature' either directly or indirectly from
several places; while it is unknown how this issue didn't break ZFS on 64-bit
little-endian powerpc, it is known to break ZFS with many Linux versions on
both 32-bit and 64-bit big-endian powerpc.

Until this issue is fixed in Linux, we have to workaround it by providing our
own version of the inline function without using jump labels.

Signed-off-by: WHR <msl0000023508@gmail.com>

config/kernel-cpu_has_feature.m4

@@ -0,0 +1,29 @@
+dnl #
+dnl # cpu_has_feature() may referencing GPL-only cpu_feature_keys on powerpc
+dnl #
+
+dnl #
+dnl # Checking if cpu_has_feature is exported GPL-only
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_CPU_HAS_FEATURE], [
+	ZFS_LINUX_TEST_SRC([cpu_has_feature], [
+		#include <linux/version.h>
+		#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 7, 0)
+		#include <asm/cpu_has_feature.h>
+		#else
+		#include <asm/cputable.h>
+		#endif
+	], [
+		return cpu_has_feature(CPU_FTR_ALTIVEC) ? 0 : 1;
+	], [], [ZFS_META_LICENSE])
+])
+AC_DEFUN([ZFS_AC_KERNEL_CPU_HAS_FEATURE], [
+	AC_MSG_CHECKING([whether cpu_has_feature() is GPL-only])
+	ZFS_LINUX_TEST_RESULT([cpu_has_feature_license], [
+		AC_MSG_RESULT(no)
+	], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_CPU_HAS_FEATURE_GPL_ONLY, 1,
+		    [cpu_has_feature() is GPL-only])
+	])
+])

config/kernel.m4

@@ -151,6 +151,11 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_IDMAP_MNT_API
 	ZFS_AC_KERNEL_SRC_IATTR_VFSID
 	ZFS_AC_KERNEL_SRC_FILEMAP
+	case "$host_cpu" in
+		powerpc*)
+			ZFS_AC_KERNEL_SRC_CPU_HAS_FEATURE
+			;;
+	esac
 
 	AC_MSG_CHECKING([for available kernel interfaces])
 	ZFS_LINUX_TEST_COMPILE_ALL([kabi])
@@ -275,6 +280,11 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_IDMAP_MNT_API
 	ZFS_AC_KERNEL_IATTR_VFSID
 	ZFS_AC_KERNEL_FILEMAP
+	case "$host_cpu" in
+		powerpc*)
+			ZFS_AC_KERNEL_CPU_HAS_FEATURE
+			;;
+	esac
 ])
 
 dnl #

include/os/linux/kernel/linux/powerpc_cpu_has_feature_compat.h

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#if defined __powerpc__ && defined CONFIG_JUMP_LABEL_FEATURE_CHECKS && \
+    defined HAVE_CPU_HAS_FEATURE_GPL_ONLY
+/*
+ * Linux 4.7 makes cpu_has_feature to use jump labels on powerpc if
+ * CONFIG_JUMP_LABEL_FEATURE_CHECKS is enabled, in this case however it
+ * references GPL-only symbol cpu_feature_keys. Therefore we overrides this
+ * interface when it is detected being GPL-only.
+ */
+
+#ifndef	__ASM_POWERPC_CPU_HAS_FEATURE_H
+#define	__ASM_POWERPC_CPU_HAS_FEATURE_H
+
+#ifndef	__ASSEMBLY__
+
+#include <asm/cputable.h>
+
+static __always_inline bool early_cpu_has_feature(unsigned long feature)
+{
+	return (!!((CPU_FTRS_ALWAYS & feature) ||
+	    (CPU_FTRS_POSSIBLE & cur_cpu_spec->cpu_features & feature)));
+}
+
+static __always_inline bool cpu_has_feature(unsigned long feature)
+{
+	return (early_cpu_has_feature(feature));
+}
+
+#endif	/* __ASSEMBLY__ */
+
+#endif	/* __ASM_POWERPC_CPU_HAS_FEATURE_H */
+
+#endif

module/icp/algs/sha2/sha256_impl.c

@@ -23,6 +23,10 @@
  * Copyright (c) 2022 Tino Reichardt <milky-zfs@mcmilk.de>
  */
 
+#if defined(__linux__) && defined(__powerpc__)
+#include <linux/powerpc_cpu_has_feature_compat.h>
+#endif
+
 #include <sys/zfs_context.h>
 #include <sys/zfs_impl.h>
 #include <sys/sha2.h>

module/icp/algs/sha2/sha512_impl.c

@@ -23,6 +23,10 @@
  * Copyright (c) 2022 Tino Reichardt <milky-zfs@mcmilk.de>
  */
 
+#if defined(__linux__) && defined(__powerpc__)
+#include <linux/powerpc_cpu_has_feature_compat.h>
+#endif
+
 #include <sys/zfs_context.h>
 #include <sys/zfs_impl.h>
 #include <sys/sha2.h>

module/os/linux/zfs/zfs_vnops_os.c

@@ -29,6 +29,9 @@
 /* Portions Copyright 2007 Jeremy Teo */
 /* Portions Copyright 2010 Robert Milkowski */
 
+#ifdef __powerpc__
+#include <linux/powerpc_cpu_has_feature_compat.h>
+#endif
 
 #include <sys/types.h>
 #include <sys/param.h>

module/os/linux/zfs/zfs_znode.c

@@ -26,6 +26,9 @@
 /* Portions Copyright 2007 Jeremy Teo */
 
 #ifdef _KERNEL
+#ifdef __powerpc__
+#include <linux/powerpc_cpu_has_feature_compat.h>
+#endif
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/time.h>

module/zfs/vdev_raidz_math_powerpc_altivec.c

@@ -29,6 +29,10 @@
 #if defined(__powerpc__)
 #pragma GCC target("altivec")
 
+#ifdef __linux__
+#include <linux/powerpc_cpu_has_feature_compat.h>
+#endif
+
 #include "vdev_raidz_math_powerpc_altivec_common.h"
 
 #define	SYN_STRIDE		4