[RESEND v4 PATCH 1/2] [PowerPC] Add simd.h implementation

[Shawn Landden <shawn@git.icu>]

Based off the x86 one.

WireGuard really wants to be able to do SIMD in interrupts,
so it can accelerate its in-bound path.

v4: allow using the may_use_simd symbol even when it always
    returns false (via include guards)
Signed-off-by: Shawn Landden <shawn@git.icu>
---
 arch/powerpc/include/asm/simd.h | 17 +++++++++++++++++
 arch/powerpc/kernel/process.c   | 30 ++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 arch/powerpc/include/asm/simd.h

diff --git a/arch/powerpc/include/asm/simd.h b/arch/powerpc/include/asm/simd.h
new file mode 100644
index 000000000..2fe26f258
--- /dev/null
+++ b/arch/powerpc/include/asm/simd.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+/*
+ * may_use_simd - whether it is allowable at this time to issue SIMD
+ *                instructions or access the SIMD register file
+ *
+ * It's always ok in process context (ie "not interrupt")
+ * but it is sometimes ok even from an irq.
+ */
+#ifdef CONFIG_PPC_FPU
+extern bool may_use_simd(void);
+#else
+static inline bool may_use_simd(void)
+{
+	return false;
+}
+#endif
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index dd9e0d538..ef534831f 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -345,6 +345,36 @@ static int restore_altivec(struct task_struct *tsk)
 	}
 	return 0;
 }
+
+/*
+ * Were we in user mode when we were
+ * interrupted?
+ *
+ * Doing kernel_altivec/vsx_begin/end() is ok if we are running
+ * in an interrupt context from user mode - we'll just
+ * save the FPU state as required.
+ */
+static bool interrupted_user_mode(void)
+{
+	struct pt_regs *regs = get_irq_regs();
+
+	return regs && user_mode(regs);
+}
+
+/*
+ * Can we use FPU in kernel mode with the
+ * whole "kernel_fpu/altivec/vsx_begin/end()" sequence?
+ *
+ * It's always ok in process context (ie "not interrupt")
+ * but it is sometimes ok even from an irq.
+ */
+bool may_use_simd(void)
+{
+	return !in_interrupt() ||
+		interrupted_user_mode();
+}
+EXPORT_SYMBOL(may_use_simd);
+
 #else
 #define loadvec(thr) 0
 static inline int restore_altivec(struct task_struct *tsk) { return 0; }
-- 
2.21.0.1020.gf2820cf01a