x86: Support for instruction breakpoints

Instruction breakpoints need to have a specific length of 0 to
be working. Bring this support but also take care the user is not
trying to set an unsupported length, like a range breakpoint for
example.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Jason Wessel <jason.wessel@windriver.com>

arch/x86/include/asm/hw_breakpoint.h

@@ -20,10 +20,10 @@ struct arch_hw_breakpoint {
 #include <linux/list.h>
 
 /* Available HW breakpoint length encodings */
+#define X86_BREAKPOINT_LEN_X		0x00
 #define X86_BREAKPOINT_LEN_1		0x40
 #define X86_BREAKPOINT_LEN_2		0x44
 #define X86_BREAKPOINT_LEN_4		0x4c
-#define X86_BREAKPOINT_LEN_EXECUTE	0x40
 
 #ifdef CONFIG_X86_64
 #define X86_BREAKPOINT_LEN_8		0x48

arch/x86/kernel/hw_breakpoint.c

@@ -208,6 +208,9 @@ int arch_bp_generic_fields(int x86_len, int x86_type,
 {
 	/* Len */
 	switch (x86_len) {
+	case X86_BREAKPOINT_LEN_X:
+		*gen_len = sizeof(long);
+		break;
 	case X86_BREAKPOINT_LEN_1:
 		*gen_len = HW_BREAKPOINT_LEN_1;
 		break;
@@ -251,6 +254,29 @@ static int arch_build_bp_info(struct perf_event *bp)
 
 	info->address = bp->attr.bp_addr;
 
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_W:
+		info->type = X86_BREAKPOINT_WRITE;
+		break;
+	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
+		info->type = X86_BREAKPOINT_RW;
+		break;
+	case HW_BREAKPOINT_X:
+		info->type = X86_BREAKPOINT_EXECUTE;
+		/*
+		 * x86 inst breakpoints need to have a specific undefined len.
+		 * But we still need to check userspace is not trying to setup
+		 * an unsupported length, to get a range breakpoint for example.
+		 */
+		if (bp->attr.bp_len == sizeof(long)) {
+			info->len = X86_BREAKPOINT_LEN_X;
+			return 0;
+		}
+	default:
+		return -EINVAL;
+	}
+
 	/* Len */
 	switch (bp->attr.bp_len) {
 	case HW_BREAKPOINT_LEN_1:
@@ -271,21 +297,6 @@ static int arch_build_bp_info(struct perf_event *bp)
 		return -EINVAL;
 	}
 
-	/* Type */
-	switch (bp->attr.bp_type) {
-	case HW_BREAKPOINT_W:
-		info->type = X86_BREAKPOINT_WRITE;
-		break;
-	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
-		info->type = X86_BREAKPOINT_RW;
-		break;
-	case HW_BREAKPOINT_X:
-		info->type = X86_BREAKPOINT_EXECUTE;
-		break;
-	default:
-		return -EINVAL;
-	}
-
 	return 0;
 }
 /*
@@ -305,6 +316,9 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
 	ret = -EINVAL;
 
 	switch (info->len) {
+	case X86_BREAKPOINT_LEN_X:
+		align = sizeof(long) -1;
+		break;
 	case X86_BREAKPOINT_LEN_1:
 		align = 0;
 		break;