From: Jinchao Wang <[email protected]> Wprobe needs to move an active per-CPU watchpoint without releasing and reserving its hardware slot.
Add arch_modify_local_hw_breakpoint_addr() as the architecture backend for modify_local_hw_breakpoint_addr(). It validates the new address, finds the installed local slot, and updates the hardware debug register and per-CPU shadow register. The core layer (modify_local_hw_breakpoint_addr()) handles updating bp->attr.bp_addr and counter_arch_bp(bp)->address. The caller must provide an installed local event and a valid address. Slot ownership, breakpoint type, length, mask and DR7 remain unchanged. Link: https://lore.kernel.org/all/59637b96946653393a7ad3c7de094094796b39c2.1785067572.git.wangjinchao...@gmail.com/ Assisted-by: Antigravity:gemini-3.8-flash Signed-off-by: Jinchao Wang <[email protected]> Signed-off-by: Masami Hiramatsu (Google) <[email protected]> --- Changes in v15: - Temporarily clear the breakpoint enable bit in DR7 before updating the debug address register, and re-enable it afterward, to comply with the x86 hardware specification and avoid spurious #DB exceptions. Changes in v13: - Add compiler barrier (barrier()) before checking cpu_dr7_seq to prevent hoisting the sequence check before set_debugreg(). - Clarify in commit log and code comment that the core layer manages updating bp->attr.bp_addr and counter_arch_bp(bp)->address. Changes in v11: - Return int error code instead of void. - Validate the new address using hw_breakpoint_arch_parse() before updating registers. - Increment cpu_dr7_seq in a sequence loop for NMI protection. - Return -ENOENT if the breakpoint slot is not found on the local CPU. --- arch/x86/include/asm/hw_breakpoint.h | 2 + arch/x86/kernel/hw_breakpoint.c | 56 ++++++++++++++++++++++++++++++++++ 2 files changed, 58 insertions(+) diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h index 0bc931cd0698..f35ec491f6dd 100644 --- a/arch/x86/include/asm/hw_breakpoint.h +++ b/arch/x86/include/asm/hw_breakpoint.h @@ -59,6 +59,8 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused, int arch_install_hw_breakpoint(struct perf_event *bp); +int arch_modify_local_hw_breakpoint_addr(struct perf_event *bp, + unsigned long addr); void arch_uninstall_hw_breakpoint(struct perf_event *bp); void hw_breakpoint_pmu_read(struct perf_event *bp); void hw_breakpoint_pmu_unthrottle(struct perf_event *bp); diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index 312550be3ad2..99f0926298a8 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -129,6 +129,62 @@ int arch_install_hw_breakpoint(struct perf_event *bp) return 0; } +/* + * Modify the address of an installed perf counter breakpoint on local CPU. + * + * This updates the debug address register and per-CPU shadow state without + * changing slot allocation or DR7. The core layer (modify_local_hw_breakpoint_addr()) + * manages updating bp->attr.bp_addr and counter_arch_bp(bp)->address. + * + * Atomic: called with IRQs disabled and handles variables and registers + * local to this CPU. + */ +int arch_modify_local_hw_breakpoint_addr(struct perf_event *bp, + unsigned long addr) +{ + struct arch_hw_breakpoint *info = counter_arch_bp(bp); + struct arch_hw_breakpoint hw; + struct perf_event_attr attr = bp->attr; + unsigned long dr7; + unsigned int seq; + int i, ret; + + lockdep_assert_irqs_disabled(); + + attr.bp_addr = addr; + ret = hw_breakpoint_arch_parse(bp, &attr, &hw); + if (ret) + return ret; + + for (i = 0; i < HBP_NUM; i++) { + if (this_cpu_read(bp_per_reg[i]) == bp) + break; + } + + if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot")) + return -ENOENT; + + do { + seq = this_cpu_inc_return(cpu_dr7_seq); + + /* Disable breakpoint in DR7 before updating address register */ + dr7 = this_cpu_read(cpu_dr7); + set_debugreg((dr7 & ~__encode_dr7(i, info->len, info->type)) | DR7_FIXED_1, 7); + barrier(); + + this_cpu_write(cpu_debugreg[i], addr); + barrier(); + set_debugreg(addr, i); + barrier(); + + /* Re-enable breakpoint in DR7 */ + set_debugreg(this_cpu_read(cpu_dr7) | DR7_FIXED_1, 7); + barrier(); + } while (seq != this_cpu_read(cpu_dr7_seq)); + + return 0; +} + /* * Uninstall the breakpoint contained in the given counter. *
