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LoongArch: Trigger user-space watchpoints correctly
In the current code, gdb can set the watchpoint successfully through ptrace interface, but watchpoint will not be triggered. When debugging the following code using gdb. lihui@bogon:~$ cat test.c #include <stdio.h> int a = 0; int main() { a = 1; printf("a = %d\n", a); return 0; } lihui@bogon:~$ gcc -g test.c -o test lihui@bogon:~$ gdb test ... (gdb) watch a ... (gdb) r ... a = 1 [Inferior 1 (process 4650) exited normally] No watchpoints were triggered, the root causes are: 1. Kernel uses perf_event and hw_breakpoint framework to control watchpoint, but the perf_event corresponding to watchpoint is not enabled. So it needs to be enabled according to MWPnCFG3 or FWPnCFG3 PLV bit field in ptrace_hbp_set_ctrl(), and privilege is set according to the monitored addr in hw_breakpoint_control(). Furthermore, add a judgment in ptrace_hbp_set_addr() to ensure kernel-space addr cannot be monitored in user mode. 2. The global enable control for all watchpoints is the WE bit of CSR.CRMD, and hardware sets the value to 0 when an exception is triggered. When the ERTN instruction is executed to return, the hardware restores the value of the PWE field of CSR.PRMD here. So, before a thread containing watchpoints be scheduled, the PWE field of CSR.PRMD needs to be set to 1. Add this modification in hw_breakpoint_control(). 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 https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#basic-control-and-status-registers With this patch: lihui@bogon:~$ gdb test ... (gdb) watch a Hardware watchpoint 1: a (gdb) r ... Hardware watchpoint 1: a Old value = 0 New value = 1 main () at test.c:6 6 printf("a = %d\n", a); (gdb) c Continuing. a = 1 [Inferior 1 (process 775) exited normally] Cc: stable@vger.kernel.org Signed-off-by: Hui Li <lihui@loongson.cn> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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3 changed files with 31 additions and 6 deletions
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@ -75,6 +75,8 @@ do { \
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#define CSR_MWPC_NUM 0x3f
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#define CTRL_PLV_ENABLE 0x1e
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#define CTRL_PLV0_ENABLE 0x02
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#define CTRL_PLV3_ENABLE 0x10
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#define MWPnCFG3_LoadEn 8
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#define MWPnCFG3_StoreEn 9
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@ -174,11 +174,21 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
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static int hw_breakpoint_control(struct perf_event *bp,
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enum hw_breakpoint_ops ops)
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{
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u32 ctrl;
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u32 ctrl, privilege;
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int i, max_slots, enable;
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struct pt_regs *regs;
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struct perf_event **slots;
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struct arch_hw_breakpoint *info = counter_arch_bp(bp);
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if (arch_check_bp_in_kernelspace(info))
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privilege = CTRL_PLV0_ENABLE;
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else
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privilege = CTRL_PLV3_ENABLE;
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/* Whether bp belongs to a task. */
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if (bp->hw.target)
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regs = task_pt_regs(bp->hw.target);
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if (info->ctrl.type == LOONGARCH_BREAKPOINT_EXECUTE) {
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/* Breakpoint */
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slots = this_cpu_ptr(bp_on_reg);
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@ -204,13 +214,15 @@ static int hw_breakpoint_control(struct perf_event *bp,
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write_wb_reg(CSR_CFG_ASID, i, 0, 0);
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write_wb_reg(CSR_CFG_ASID, i, 1, 0);
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if (info->ctrl.type == LOONGARCH_BREAKPOINT_EXECUTE) {
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write_wb_reg(CSR_CFG_CTRL, i, 0, CTRL_PLV_ENABLE);
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write_wb_reg(CSR_CFG_CTRL, i, 0, privilege);
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} else {
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ctrl = encode_ctrl_reg(info->ctrl);
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write_wb_reg(CSR_CFG_CTRL, i, 1, ctrl | CTRL_PLV_ENABLE);
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write_wb_reg(CSR_CFG_CTRL, i, 1, ctrl | privilege);
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}
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enable = csr_read64(LOONGARCH_CSR_CRMD);
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csr_write64(CSR_CRMD_WE | enable, LOONGARCH_CSR_CRMD);
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if (bp->hw.target)
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regs->csr_prmd |= CSR_PRMD_PWE;
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break;
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case HW_BREAKPOINT_UNINSTALL:
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/* Reset the FWPnCFG/MWPnCFG 1~4 register. */
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@ -222,6 +234,8 @@ static int hw_breakpoint_control(struct perf_event *bp,
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write_wb_reg(CSR_CFG_CTRL, i, 1, 0);
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write_wb_reg(CSR_CFG_ASID, i, 0, 0);
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write_wb_reg(CSR_CFG_ASID, i, 1, 0);
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if (bp->hw.target)
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regs->csr_prmd &= ~CSR_PRMD_PWE;
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break;
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}
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@ -608,9 +608,14 @@ static int ptrace_hbp_set_ctrl(unsigned int note_type,
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return -EINVAL;
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}
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err = ptrace_hbp_fill_attr_ctrl(note_type, ctrl, &attr);
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if (err)
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return err;
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if (uctrl & CTRL_PLV_ENABLE) {
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err = ptrace_hbp_fill_attr_ctrl(note_type, ctrl, &attr);
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if (err)
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return err;
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attr.disabled = 0;
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} else {
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attr.disabled = 1;
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}
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return modify_user_hw_breakpoint(bp, &attr);
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}
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@ -641,6 +646,10 @@ static int ptrace_hbp_set_addr(unsigned int note_type,
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struct perf_event *bp;
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struct perf_event_attr attr;
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/* Kernel-space address cannot be monitored by user-space */
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if ((unsigned long)addr >= XKPRANGE)
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return -EINVAL;
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bp = ptrace_hbp_get_initialised_bp(note_type, tsk, idx);
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if (IS_ERR(bp))
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return PTR_ERR(bp);
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