powerpc/64s: Add support for software count cache flush

commit ee13cb249fabdff8b90aaff61add347749280087 upstream.

Some CPU revisions support a mode where the count cache needs to be
flushed by software on context switch. Additionally some revisions may
have a hardware accelerated flush, in which case the software flush
sequence can be shortened.

If we detect the appropriate flag from firmware we patch a branch
into _switch() which takes us to a count cache flush sequence.

That sequence in turn may be patched to return early if we detect that
the CPU supports accelerating the flush sequence in hardware.

Add debugfs support for reporting the state of the flush, as well as
runtime disabling it.

And modify the spectre_v2 sysfs file to report the state of the
software flush.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/asm-prototypes.h b/arch/powerpc/include/asm/asm-prototypes.h
new file mode 100644
index 000000000000..8944c55591cf
--- /dev/null
+++ b/arch/powerpc/include/asm/asm-prototypes.h
@@ -0,0 +1,21 @@
+#ifndef _ASM_POWERPC_ASM_PROTOTYPES_H
+#define _ASM_POWERPC_ASM_PROTOTYPES_H
+/*
+ * This file is for prototypes of C functions that are only called
+ * from asm, and any associated variables.
+ *
+ * Copyright 2016, Daniel Axtens, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ */
+
+/* Patch sites */
+extern s32 patch__call_flush_count_cache;
+extern s32 patch__flush_count_cache_return;
+
+extern long flush_count_cache;
+
+#endif /* _ASM_POWERPC_ASM_PROTOTYPES_H */