s390: introduce CPU alternatives

Implement CPU alternatives, which allows to optionally patch newer
instructions at runtime, based on CPU facilities availability.

A new kernel boot parameter "noaltinstr" disables patching.

Current implementation is derived from x86 alternatives. Although
ideal instructions padding (when altinstr is longer then oldinstr)
is added at compile time, and no oldinstr nops optimization has to be
done at runtime. Also couple of compile time sanity checks are done:
1. oldinstr and altinstr must be <= 254 bytes long,
2. oldinstr and altinstr must not have an odd length.

alternative(oldinstr, altinstr, facility);
alternative_2(oldinstr, altinstr1, facility1, altinstr2, facility2);

Both compile time and runtime padding consists of either 6/4/2 bytes nop
or a jump (brcl) + 2 bytes nop filler if padding is longer then 6 bytes.

.altinstructions and .altinstr_replacement sections are part of
__init_begin : __init_end region and are freed after initialization.

Signed-off-by: Vasily Gorbik <gor@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 163 insertions, 0 deletions

diff --git a/arch/s390/include/asm/alternative.h b/arch/s390/include/asm/alternative.h
new file mode 100644
index 000000000000..6c268f6a51d3
--- /dev/null
+++ b/arch/s390/include/asm/alternative.h
@@ -0,0 +1,163 @@
+#ifndef _ASM_S390_ALTERNATIVE_H
+#define _ASM_S390_ALTERNATIVE_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+#include <linux/stddef.h>
+#include <linux/stringify.h>
+
+struct alt_instr {
+	s32 instr_offset;	/* original instruction */
+	s32 repl_offset;	/* offset to replacement instruction */
+	u16 facility;		/* facility bit set for replacement */
+	u8  instrlen;		/* length of original instruction */
+	u8  replacementlen;	/* length of new instruction */
+} __packed;
+
+#ifdef CONFIG_ALTERNATIVES
+extern void apply_alternative_instructions(void);
+extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
+#else
+static inline void apply_alternative_instructions(void) {};
+static inline void apply_alternatives(struct alt_instr *start,
+				      struct alt_instr *end) {};
+#endif
+/*
+ * |661:       |662:	  |6620      |663:
+ * +-----------+---------------------+
+ * | oldinstr  | oldinstr_padding    |
+ * |	       +----------+----------+
+ * |	       |	  |	     |
+ * |	       | >6 bytes |6/4/2 nops|
+ * |	       |6 bytes jg----------->
+ * +-----------+---------------------+
+ *		 ^^ static padding ^^
+ *
+ * .altinstr_replacement section
+ * +---------------------+-----------+
+ * |6641:			     |6651:
+ * | alternative instr 1	     |
+ * +-----------+---------+- - - - - -+
+ * |6642:		 |6652:      |
+ * | alternative instr 2 | padding
+ * +---------------------+- - - - - -+
+ *			  ^ runtime ^
+ *
+ * .altinstructions section
+ * +---------------------------------+
+ * | alt_instr entries for each      |
+ * | alternative instr		     |
+ * +---------------------------------+
+ */
+
+#define b_altinstr(num)	"664"#num
+#define e_altinstr(num)	"665"#num
+
+#define e_oldinstr_pad_end	"663"
+#define oldinstr_len		"662b-661b"
+#define oldinstr_total_len	e_oldinstr_pad_end"b-661b"
+#define altinstr_len(num)	e_altinstr(num)"b-"b_altinstr(num)"b"
+#define oldinstr_pad_len(num) \
+	"-(((" altinstr_len(num) ")-(" oldinstr_len ")) > 0) * " \
+	"((" altinstr_len(num) ")-(" oldinstr_len "))"
+
+#define INSTR_LEN_SANITY_CHECK(len)					\
+	".if " len " > 254\n"						\
+	"\t.error \"cpu alternatives does not support instructions "	\
+		"blocks > 254 bytes\"\n"				\
+	".endif\n"							\
+	".if (" len ") %% 2\n"						\
+	"\t.error \"cpu alternatives instructions length is odd\"\n"	\
+	".endif\n"
+
+#define OLDINSTR_PADDING(oldinstr, num)					\
+	".if " oldinstr_pad_len(num) " > 6\n"				\
+	"\tjg " e_oldinstr_pad_end "f\n"				\
+	"6620:\n"							\
+	"\t.fill (" oldinstr_pad_len(num) " - (6620b-662b)) / 2, 2, 0x0700\n" \
+	".else\n"							\
+	"\t.fill " oldinstr_pad_len(num) " / 6, 6, 0xc0040000\n"	\
+	"\t.fill " oldinstr_pad_len(num) " %% 6 / 4, 4, 0x47000000\n"	\
+	"\t.fill " oldinstr_pad_len(num) " %% 6 %% 4 / 2, 2, 0x0700\n"	\
+	".endif\n"
+
+#define OLDINSTR(oldinstr, num)						\
+	"661:\n\t" oldinstr "\n662:\n"					\
+	OLDINSTR_PADDING(oldinstr, num)					\
+	e_oldinstr_pad_end ":\n"					\
+	INSTR_LEN_SANITY_CHECK(oldinstr_len)
+
+#define OLDINSTR_2(oldinstr, num1, num2)				\
+	"661:\n\t" oldinstr "\n662:\n"					\
+	".if " altinstr_len(num1) " < " altinstr_len(num2) "\n"		\
+	OLDINSTR_PADDING(oldinstr, num2)				\
+	".else\n"							\
+	OLDINSTR_PADDING(oldinstr, num1)				\
+	".endif\n"							\
+	e_oldinstr_pad_end ":\n"					\
+	INSTR_LEN_SANITY_CHECK(oldinstr_len)
+
+#define ALTINSTR_ENTRY(facility, num)					\
+	"\t.long 661b - .\n"			/* old instruction */	\
+	"\t.long " b_altinstr(num)"b - .\n"	/* alt instruction */	\
+	"\t.word " __stringify(facility) "\n"	/* facility bit    */	\
+	"\t.byte " oldinstr_total_len "\n"	/* source len	   */	\
+	"\t.byte " altinstr_len(num) "\n"	/* alt instruction len */
+
+#define ALTINSTR_REPLACEMENT(altinstr, num)	/* replacement */	\
+	b_altinstr(num)":\n\t" altinstr "\n" e_altinstr(num) ":\n"	\
+	INSTR_LEN_SANITY_CHECK(altinstr_len(num))
+
+#ifdef CONFIG_ALTERNATIVES
+/* alternative assembly primitive: */
+#define ALTERNATIVE(oldinstr, altinstr, facility) \
+	".pushsection .altinstr_replacement, \"ax\"\n"			\
+	ALTINSTR_REPLACEMENT(altinstr, 1)				\
+	".popsection\n"							\
+	OLDINSTR(oldinstr, 1)						\
+	".pushsection .altinstructions,\"a\"\n"				\
+	ALTINSTR_ENTRY(facility, 1)					\
+	".popsection\n"
+
+#define ALTERNATIVE_2(oldinstr, altinstr1, facility1, altinstr2, facility2)\
+	".pushsection .altinstr_replacement, \"ax\"\n"			\
+	ALTINSTR_REPLACEMENT(altinstr1, 1)				\
+	ALTINSTR_REPLACEMENT(altinstr2, 2)				\
+	".popsection\n"							\
+	OLDINSTR_2(oldinstr, 1, 2)					\
+	".pushsection .altinstructions,\"a\"\n"				\
+	ALTINSTR_ENTRY(facility1, 1)					\
+	ALTINSTR_ENTRY(facility2, 2)					\
+	".popsection\n"
+#else
+/* Alternative instructions are disabled, let's put just oldinstr in */
+#define ALTERNATIVE(oldinstr, altinstr, facility) \
+	oldinstr "\n"
+
+#define ALTERNATIVE_2(oldinstr, altinstr1, facility1, altinstr2, facility2) \
+	oldinstr "\n"
+#endif
+
+/*
+ * Alternative instructions for different CPU types or capabilities.
+ *
+ * This allows to use optimized instructions even on generic binary
+ * kernels.
+ *
+ * oldinstr is padded with jump and nops at compile time if altinstr is
+ * longer. altinstr is padded with jump and nops at run-time during patching.
+ *
+ * For non barrier like inlines please define new variants
+ * without volatile and memory clobber.
+ */
+#define alternative(oldinstr, altinstr, facility)			\
+	asm volatile(ALTERNATIVE(oldinstr, altinstr, facility) : : : "memory")
+
+#define alternative_2(oldinstr, altinstr1, facility1, altinstr2, facility2) \
+	asm volatile(ALTERNATIVE_2(oldinstr, altinstr1, facility1,	    \
+				   altinstr2, facility2) ::: "memory")
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _ASM_S390_ALTERNATIVE_H */