LoongArch: Fix multiple hardware watchpoint issues

In the current code, if multiple hardware breakpoints/watchpoints in
a user-space thread, some of them will not be triggered.

When debugging the following code using gdb.

lihui@bogon:~$ cat test.c
  #include <stdio.h>
  int a = 0;
  int main()
  {
    printf("start test\n");
    a = 1;
    printf("a = %d\n", a);
    printf("end test\n");
    return 0;
  }
lihui@bogon:~$ gcc -g test.c -o test
lihui@bogon:~$ gdb test
...
(gdb) start
...
Temporary breakpoint 1, main () at test.c:5
5        printf("start test\n");
(gdb) watch a
Hardware watchpoint 2: a
(gdb) hbreak 8
Hardware assisted breakpoint 3 at 0x1200006ec: file test.c, line 8.
(gdb) c
Continuing.
start test
a = 1

Breakpoint 3, main () at test.c:8
8        printf("end test\n");
...

The first hardware watchpoint is not triggered, the root causes are:

1. In hw_breakpoint_control(), The FWPnCFG1.2.4/MWPnCFG1.2.4 register
   settings are not distinguished. They should be set based on hardware
   watchpoint functions (fetch or load/store operations).

2. In breakpoint_handler() and watchpoint_handler(), it doesn't identify
   which watchpoint is triggered. So, all watchpoint-related perf_event
   callbacks are called and siginfo is sent to the user space. This will
   cause user-space unable to determine which watchpoint is triggered.
   The kernel need to identity which watchpoint is triggered via MWPS/
   FWPS registers, and then call the corresponding perf event callbacks
   to report siginfo to the user-space.

Modify the relevant code to solve above issues.

All changes according to the LoongArch Reference Manual:
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#control-and-status-registers-related-to-watchpoints

With this patch:

lihui@bogon:~$ gdb test
...
(gdb) start
...
Temporary breakpoint 1, main () at test.c:5
5        printf("start test\n");
(gdb) watch a
Hardware watchpoint 2: a
(gdb) hbreak 8
Hardware assisted breakpoint 3 at 0x1200006ec: file test.c, line 8.
(gdb) c
Continuing.
start test

Hardware watchpoint 2: a

Old value = 0
New value = 1
main () at test.c:7
7        printf("a = %d\n", a);
(gdb) c
Continuing.
a = 1

Breakpoint 3, main () at test.c:8
8        printf("end test\n");
(gdb) c
Continuing.
end test
[Inferior 1 (process 778) exited normally]

Cc: stable@vger.kernel.org
Signed-off-by: Hui Li <lihui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: lhloongson

arch/loongarch/kernel/hw_breakpoint.c

@@ -207,15 +207,15 @@ static int hw_breakpoint_control(struct perf_event *bp,
 	switch (ops) {
 	case HW_BREAKPOINT_INSTALL:
 		/* Set the FWPnCFG/MWPnCFG 1~4 register. */
-		write_wb_reg(CSR_CFG_ADDR, i, 0, info->address);
-		write_wb_reg(CSR_CFG_ADDR, i, 1, info->address);
-		write_wb_reg(CSR_CFG_MASK, i, 0, info->mask);
-		write_wb_reg(CSR_CFG_MASK, i, 1, info->mask);
-		write_wb_reg(CSR_CFG_ASID, i, 0, 0);
-		write_wb_reg(CSR_CFG_ASID, i, 1, 0);
 		if (info->ctrl.type == LOONGARCH_BREAKPOINT_EXECUTE) {
+			write_wb_reg(CSR_CFG_ADDR, i, 0, info->address);
+			write_wb_reg(CSR_CFG_MASK, i, 0, info->mask);
+			write_wb_reg(CSR_CFG_ASID, i, 0, 0);
 			write_wb_reg(CSR_CFG_CTRL, i, 0, privilege);
 		} else {
+			write_wb_reg(CSR_CFG_ADDR, i, 1, info->address);
+			write_wb_reg(CSR_CFG_MASK, i, 1, info->mask);
+			write_wb_reg(CSR_CFG_ASID, i, 1, 0);
 			ctrl = encode_ctrl_reg(info->ctrl);
 			write_wb_reg(CSR_CFG_CTRL, i, 1, ctrl | privilege);
 		}
@@ -226,14 +226,17 @@ static int hw_breakpoint_control(struct perf_event *bp,
 		break;
 	case HW_BREAKPOINT_UNINSTALL:
 		/* Reset the FWPnCFG/MWPnCFG 1~4 register. */
-		write_wb_reg(CSR_CFG_ADDR, i, 0, 0);
-		write_wb_reg(CSR_CFG_ADDR, i, 1, 0);
-		write_wb_reg(CSR_CFG_MASK, i, 0, 0);
-		write_wb_reg(CSR_CFG_MASK, i, 1, 0);
-		write_wb_reg(CSR_CFG_CTRL, i, 0, 0);
-		write_wb_reg(CSR_CFG_CTRL, i, 1, 0);
-		write_wb_reg(CSR_CFG_ASID, i, 0, 0);
-		write_wb_reg(CSR_CFG_ASID, i, 1, 0);
+		if (info->ctrl.type == LOONGARCH_BREAKPOINT_EXECUTE) {
+			write_wb_reg(CSR_CFG_ADDR, i, 0, 0);
+			write_wb_reg(CSR_CFG_MASK, i, 0, 0);
+			write_wb_reg(CSR_CFG_CTRL, i, 0, 0);
+			write_wb_reg(CSR_CFG_ASID, i, 0, 0);
+		} else {
+			write_wb_reg(CSR_CFG_ADDR, i, 1, 0);
+			write_wb_reg(CSR_CFG_MASK, i, 1, 0);
+			write_wb_reg(CSR_CFG_CTRL, i, 1, 0);
+			write_wb_reg(CSR_CFG_ASID, i, 1, 0);
+		}
 		if (bp->hw.target)
 			regs->csr_prmd &= ~CSR_PRMD_PWE;
 		break;
@@ -476,12 +479,15 @@ void breakpoint_handler(struct pt_regs *regs)
 	slots = this_cpu_ptr(bp_on_reg);
 
 	for (i = 0; i < boot_cpu_data.watch_ireg_count; ++i) {
-		bp = slots[i];
-		if (bp == NULL)
-			continue;
-		perf_bp_event(bp, regs);
+		if ((csr_read32(LOONGARCH_CSR_FWPS) & (0x1 << i))) {
+			bp = slots[i];
+			if (bp == NULL)
+				continue;
+			perf_bp_event(bp, regs);
+			csr_write32(0x1 << i, LOONGARCH_CSR_FWPS);
+			update_bp_registers(regs, 0, 0);
+		}
 	}
-	update_bp_registers(regs, 0, 0);
 }
 NOKPROBE_SYMBOL(breakpoint_handler);
 
@@ -493,12 +499,15 @@ void watchpoint_handler(struct pt_regs *regs)
 	slots = this_cpu_ptr(wp_on_reg);
 
 	for (i = 0; i < boot_cpu_data.watch_dreg_count; ++i) {
-		wp = slots[i];
-		if (wp == NULL)
-			continue;
-		perf_bp_event(wp, regs);
+		if ((csr_read32(LOONGARCH_CSR_MWPS) & (0x1 << i))) {
+			wp = slots[i];
+			if (wp == NULL)
+				continue;
+			perf_bp_event(wp, regs);
+			csr_write32(0x1 << i, LOONGARCH_CSR_MWPS);
+			update_bp_registers(regs, 0, 1);
+		}
 	}
-	update_bp_registers(regs, 0, 1);
 }
 NOKPROBE_SYMBOL(watchpoint_handler);