s390/alternatives: Add debug functionality

Similar to x86 and loongarch add a "debug-alternative" command line
parameter, which allows for alternative debugging. The parameter
itself comes with architecture specific semantics:

"debug-alternative"
 -> print debug message for every single alternative

"debug-alternative=0;2"
-> print debug message for all alternatives with type 0 and 2

"debug-alternative=0:0-7"
-> print debug message for all alternatives with type 0 which have a
   facility number within the range of 0-7

"debug-alternative=0:!8;1"
-> print debug message for all alternatives with type 0, for all
   facility numbers, except facility 8, and in addition print all
   alternatives with type 1

A defconfig build currently results in a kernel with more than 20.000
alternatives, where the majority is for the niai alternative (spinlocks),
and the relocated lowcore alternative. The following kernel command like
options limit alternative debug output, and enable dynamic debug messages:

debug-alternative=0:!49;1:!0
earlyprintk
bootdebug
ignore_loglevel
loglevel=8
dyndbg="file alternative.c +p"

This results in output like this:

 alt: [0/ 11] 0000021b9ce8680c: c0f400000089 -> c00400000000
 alt: [0/ 64] 0000021b9ce87e60: c0f400000043 -> c00400000000
 alt: [0/133] 0000021b9ce88c56: c0f400000027 -> c00400000000
 alt: [0/ 74] 0000021b9ce89410: c0f40000002a -> c00400000000
 alt: [0/ 40] 0000021b9dc3720a: 47000000 -> b280d398
 alt: [0/193] 0000021b9dc37306: 47000000 -> b201d2b0
 alt: [0/193] 0000021b9dc37354: c00400000000 -> d20720c0d2b0
 alt: [1/  5] 0000038d720d7bf2: c0f400000016 -> c00400000000

With

[<alternative type>/<alternative data>] <address> oldcode -> newcode

Alternative data depends on the alternative type: for type 0
(ALT_TYPE_FACILITY) data is the facility. For type 1 (ALT_TYPE_FEATURE)
data is the corresponding machine feature.

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/boot/alternative.c

@@ -1,3 +1,138 @@
 // SPDX-License-Identifier: GPL-2.0
+#define boot_fmt(fmt)	"alt: " fmt
+#include "boot.h"
+
+#define a_debug		boot_debug
 
 #include "../kernel/alternative.c"
+
+static void alt_debug_all(int type)
+{
+	int i;
+
+	switch (type) {
+	case ALT_TYPE_FACILITY:
+		for (i = 0; i < ARRAY_SIZE(alt_debug.facilities); i++)
+			alt_debug.facilities[i] = -1UL;
+		break;
+	case ALT_TYPE_FEATURE:
+		for (i = 0; i < ARRAY_SIZE(alt_debug.mfeatures); i++)
+			alt_debug.mfeatures[i] = -1UL;
+		break;
+	case ALT_TYPE_SPEC:
+		alt_debug.spec = 1;
+		break;
+	}
+}
+
+static void alt_debug_modify(int type, unsigned int nr, bool clear)
+{
+	switch (type) {
+	case ALT_TYPE_FACILITY:
+		if (clear)
+			__clear_facility(nr, alt_debug.facilities);
+		else
+			__set_facility(nr, alt_debug.facilities);
+		break;
+	case ALT_TYPE_FEATURE:
+		if (clear)
+			__clear_machine_feature(nr, alt_debug.mfeatures);
+		else
+			__set_machine_feature(nr, alt_debug.mfeatures);
+		break;
+	}
+}
+
+static char *alt_debug_parse(int type, char *str)
+{
+	unsigned long val, endval;
+	char *endp;
+	bool clear;
+	int i;
+
+	if (*str == ':') {
+		str++;
+	} else {
+		alt_debug_all(type);
+		return str;
+	}
+	clear = false;
+	if (*str == '!') {
+		alt_debug_all(type);
+		clear = true;
+		str++;
+	}
+	while (*str) {
+		val = simple_strtoull(str, &endp, 0);
+		if (str == endp)
+			break;
+		str = endp;
+		if (*str == '-') {
+			str++;
+			endval = simple_strtoull(str, &endp, 0);
+			if (str == endp)
+				break;
+			str = endp;
+			while (val <= endval) {
+				alt_debug_modify(type, val, clear);
+				val++;
+			}
+		} else {
+			alt_debug_modify(type, val, clear);
+		}
+		if (*str != ',')
+			break;
+		str++;
+	}
+	return str;
+}
+
+/*
+ * Use debug-alternative command line parameter for debugging:
+ * "debug-alternative"
+ *  -> print debug message for every single alternative
+ *
+ * "debug-alternative=0;2"
+ * -> print debug message for all alternatives with type 0 and 2
+ *
+ * "debug-alternative=0:0-7"
+ * -> print debug message for all alternatives with type 0 and with
+ *    facility numbers within the range of 0-7
+ *    (if type 0 is ALT_TYPE_FACILITY)
+ *
+ * "debug-alternative=0:!8;1"
+ * -> print debug message for all alternatives with type 0, for all
+ *    facility number, except facility 8, and in addition print all
+ *    alternatives with type 1
+ */
+void alt_debug_setup(char *str)
+{
+	unsigned long type;
+	char *endp;
+	int i;
+
+	if (!str) {
+		alt_debug_all(ALT_TYPE_FACILITY);
+		alt_debug_all(ALT_TYPE_FEATURE);
+		alt_debug_all(ALT_TYPE_SPEC);
+		return;
+	}
+	while (*str) {
+		type = simple_strtoull(str, &endp, 0);
+		if (str == endp)
+			break;
+		str = endp;
+		switch (type) {
+		case ALT_TYPE_FACILITY:
+		case ALT_TYPE_FEATURE:
+			str = alt_debug_parse(type, str);
+			break;
+		case ALT_TYPE_SPEC:
+			alt_debug_all(ALT_TYPE_SPEC);
+			break;
+		}
+		if (*str != ';')
+			break;
+		str++;
+	}
+}

arch/s390/boot/boot.h

@@ -64,6 +64,7 @@ void parse_boot_command_line(void);
 void verify_facilities(void);
 void print_missing_facilities(void);
 void sclp_early_setup_buffer(void);
+void alt_debug_setup(char *str);
 void print_pgm_check_info(void);
 unsigned long randomize_within_range(unsigned long size, unsigned long align,
 				     unsigned long min, unsigned long max);

arch/s390/boot/ipl_parm.c

@@ -296,6 +296,9 @@ void parse_boot_command_line(void)
 		if (!strcmp(param, "facilities") && val)
 			modify_fac_list(val);
 
+		if (!strcmp(param, "debug-alternative"))
+			alt_debug_setup(val);
+
 		if (!strcmp(param, "nokaslr"))
 			__kaslr_enabled = 0;
 

arch/s390/kernel/alternative.c

@@ -1,6 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#ifndef pr_fmt
+#define pr_fmt(fmt)	"alt: " fmt
+#endif
+
 #include <linux/uaccess.h>
+#include <linux/printk.h>
 #include <asm/nospec-branch.h>
 #include <asm/abs_lowcore.h>
 #include <asm/alternative.h>
@@ -8,38 +13,78 @@
 #include <asm/sections.h>
 #include <asm/machine.h>
 
+#ifndef a_debug
+#define a_debug		pr_debug
+#endif
+
+#ifndef __kernel_va
+#define __kernel_va(x)	(void *)(x)
+#endif
+
 unsigned long __bootdata_preserved(machine_features[1]);
 
+struct alt_debug {
+	unsigned long facilities[MAX_FACILITY_BIT / BITS_PER_LONG];
+	unsigned long mfeatures[MAX_MFEATURE_BIT / BITS_PER_LONG];
+	int spec;
+};
+
+static struct alt_debug __bootdata_preserved(alt_debug);
+
+static void alternative_dump(u8 *old, u8 *new, unsigned int len, unsigned int type, unsigned int data)
+{
+	char oinsn[33], ninsn[33];
+	unsigned long kptr;
+	unsigned int pos;
+
+	for (pos = 0; pos < len && 2 * pos < sizeof(oinsn) - 3; pos++)
+		hex_byte_pack(&oinsn[2 * pos], old[pos]);
+	oinsn[2 * pos] = 0;
+	for (pos = 0; pos < len && 2 * pos < sizeof(ninsn) - 3; pos++)
+		hex_byte_pack(&ninsn[2 * pos], new[pos]);
+	ninsn[2 * pos] = 0;
+	kptr = (unsigned long)__kernel_va(old);
+	a_debug("[%d/%3d] %016lx: %s -> %s\n", type, data, kptr, oinsn, ninsn);
+}
+
 void __apply_alternatives(struct alt_instr *start, struct alt_instr *end, unsigned int ctx)
 {
-	u8 *instr, *replacement;
+	struct alt_debug *d;
 	struct alt_instr *a;
-	bool replace;
+	bool debug, replace;
+	u8 *old, *new;
 
 	/*
 	 * The scan order should be from start to end. A later scanned
 	 * alternative code can overwrite previously scanned alternative code.
 	 */
+	d = &alt_debug;
 	for (a = start; a < end; a++) {
 		if (!(a->ctx & ctx))
 			continue;
 		switch (a->type) {
 		case ALT_TYPE_FACILITY:
 			replace = test_facility(a->data);
+			debug = __test_facility(a->data, d->facilities);
 			break;
 		case ALT_TYPE_FEATURE:
 			replace = test_machine_feature(a->data);
+			debug = __test_machine_feature(a->data, d->mfeatures);
 			break;
 		case ALT_TYPE_SPEC:
 			replace = nobp_enabled();
+			debug = d->spec;
 			break;
 		default:
 			replace = false;
+			debug = false;
 		}
 		if (!replace)
 			continue;
-		instr = (u8 *)&a->instr_offset + a->instr_offset;
-		replacement = (u8 *)&a->repl_offset + a->repl_offset;
-		s390_kernel_write(instr, replacement, a->instrlen);
+		old = (u8 *)&a->instr_offset + a->instr_offset;
+		new = (u8 *)&a->repl_offset + a->repl_offset;
+		if (debug)
+			alternative_dump(old, new, a->instrlen, a->type, a->data);
+		s390_kernel_write(old, new, a->instrlen);
 	}
 }

arch/s390/kernel/early.c

@@ -55,6 +55,7 @@ decompressor_handled_param(nokaslr);
 decompressor_handled_param(cmma);
 decompressor_handled_param(relocate_lowcore);
 decompressor_handled_param(bootdebug);
+__decompressor_handled_param(debug_alternative, debug-alternative);
 #if IS_ENABLED(CONFIG_KVM)
 decompressor_handled_param(prot_virt);
 #endif