Hi Jinchao, On Wed, 10 Sep 2025 13:23:10 +0800 Jinchao Wang <[email protected]> wrote:
> Introduce arch_reinstall_hw_breakpoint() to update hardware breakpoint > parameters (address, length, type) without freeing and reallocating the > debug register slot. > > This allows atomic updates in contexts where memory allocation is not > permitted, such as kprobe handlers. > > Signed-off-by: Jinchao Wang <[email protected]> > --- > arch/x86/include/asm/hw_breakpoint.h | 1 + > arch/x86/kernel/hw_breakpoint.c | 50 ++++++++++++++++++++++++++++ > 2 files changed, 51 insertions(+) > > diff --git a/arch/x86/include/asm/hw_breakpoint.h > b/arch/x86/include/asm/hw_breakpoint.h > index 0bc931cd0698..bb7c70ad22fe 100644 > --- a/arch/x86/include/asm/hw_breakpoint.h > +++ b/arch/x86/include/asm/hw_breakpoint.h > @@ -59,6 +59,7 @@ extern int hw_breakpoint_exceptions_notify(struct > notifier_block *unused, > > > int arch_install_hw_breakpoint(struct perf_event *bp); > +int arch_reinstall_hw_breakpoint(struct perf_event *bp); > 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 b01644c949b2..89135229ed21 100644 > --- a/arch/x86/kernel/hw_breakpoint.c > +++ b/arch/x86/kernel/hw_breakpoint.c > @@ -132,6 +132,56 @@ int arch_install_hw_breakpoint(struct perf_event *bp) > return 0; > } > > +/* > + * Reinstall a hardware breakpoint on the current CPU. > + * > + * This function is used to re-establish a perf counter hardware breakpoint. > + * It finds the debug address register slot previously allocated for the > + * breakpoint and re-enables it by writing the address to the debug register > + * and setting the corresponding bits in the debug control register (DR7). > + * > + * It is expected that the breakpoint's event context lock is already held > + * and interrupts are disabled, ensuring atomicity and safety from other > + * event handlers. > + */ > +int arch_reinstall_hw_breakpoint(struct perf_event *bp) > +{ > + struct arch_hw_breakpoint *info = counter_arch_bp(bp); > + unsigned long *dr7; > + int i; > + > + lockdep_assert_irqs_disabled(); > + > + for (i = 0; i < HBP_NUM; i++) { > + struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]); > + > + if (*slot == bp) > + break; > + } > + > + if (WARN_ONCE(i == HBP_NUM, "Can't find a matching breakpoint slot")) > + return -EINVAL; > + > + set_debugreg(info->address, i); > + __this_cpu_write(cpu_debugreg[i], info->address); > + > + dr7 = this_cpu_ptr(&cpu_dr7); > + *dr7 |= encode_dr7(i, info->len, info->type); > + > + /* > + * Ensure we first write cpu_dr7 before we set the DR7 register. > + * This ensures an NMI never see cpu_dr7 0 when DR7 is not. > + */ > + barrier(); > + > + set_debugreg(*dr7, 7); > + if (info->mask) > + amd_set_dr_addr_mask(info->mask, i); > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(arch_reinstall_hw_breakpoint); Please do not expose the arch dependent symbol. Instead, you should expose an arch independent wrapper. Anyway, you also need to share the same code with arch_install_hw_breakpoint() like below; Thanks, diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index 89135229ed21..2f3c5406999e 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -84,6 +84,28 @@ int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type) return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3; } +static void __arch_install_hw_breakpoint(struct perf_event *bp, int regno) +{ + struct arch_hw_breakpoint *info = counter_arch_bp(bp); + unsigned long *dr7; + + set_debugreg(info->address, regno); + __this_cpu_write(cpu_debugreg[i], info->address); + + dr7 = this_cpu_ptr(&cpu_dr7); + *dr7 |= encode_dr7(i, info->len, info->type); + + /* + * Ensure we first write cpu_dr7 before we set the DR7 register. + * This ensures an NMI never see cpu_dr7 0 when DR7 is not. + */ + barrier(); + + set_debugreg(*dr7, 7); + if (info->mask) + amd_set_dr_addr_mask(info->mask, i); +} + /* * Install a perf counter breakpoint. * @@ -95,8 +117,6 @@ int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type) */ int arch_install_hw_breakpoint(struct perf_event *bp) { - struct arch_hw_breakpoint *info = counter_arch_bp(bp); - unsigned long *dr7; int i; lockdep_assert_irqs_disabled(); @@ -113,22 +133,7 @@ int arch_install_hw_breakpoint(struct perf_event *bp) if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot")) return -EBUSY; - set_debugreg(info->address, i); - __this_cpu_write(cpu_debugreg[i], info->address); - - dr7 = this_cpu_ptr(&cpu_dr7); - *dr7 |= encode_dr7(i, info->len, info->type); - - /* - * Ensure we first write cpu_dr7 before we set the DR7 register. - * This ensures an NMI never see cpu_dr7 0 when DR7 is not. - */ - barrier(); - - set_debugreg(*dr7, 7); - if (info->mask) - amd_set_dr_addr_mask(info->mask, i); - + __arch_install_hw_breakpoint(bp, i); return 0; } @@ -146,8 +151,6 @@ int arch_install_hw_breakpoint(struct perf_event *bp) */ int arch_reinstall_hw_breakpoint(struct perf_event *bp) { - struct arch_hw_breakpoint *info = counter_arch_bp(bp); - unsigned long *dr7; int i; lockdep_assert_irqs_disabled(); @@ -162,22 +165,7 @@ int arch_reinstall_hw_breakpoint(struct perf_event *bp) if (WARN_ONCE(i == HBP_NUM, "Can't find a matching breakpoint slot")) return -EINVAL; - set_debugreg(info->address, i); - __this_cpu_write(cpu_debugreg[i], info->address); - - dr7 = this_cpu_ptr(&cpu_dr7); - *dr7 |= encode_dr7(i, info->len, info->type); - - /* - * Ensure we first write cpu_dr7 before we set the DR7 register. - * This ensures an NMI never see cpu_dr7 0 when DR7 is not. - */ - barrier(); - - set_debugreg(*dr7, 7); - if (info->mask) - amd_set_dr_addr_mask(info->mask, i); - + __arch_install_hw_breakpoint(bp, i); return 0; } EXPORT_SYMBOL_GPL(arch_reinstall_hw_breakpoint); -- Masami Hiramatsu (Google) <[email protected]>
