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Rao" , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , kasan-dev@googlegroups.com, "David S. Miller" , Steven Rostedt , Mathieu Desnoyers , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 01/19] x86/hw_breakpoint: introduce arch_reinstall_hw_breakpoint() for atomic context Message-Id: <20250911094609.5f30e9767ffc3040068ed052@kernel.org> In-Reply-To: <20250910052335.1151048-2-wangjinchao600@gmail.com> References: <20250910052335.1151048-1-wangjinchao600@gmail.com> <20250910052335.1151048-2-wangjinchao600@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: EFD0240002 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: kyfo65n3r7hj3oabzjnoubz5c3swojqy X-HE-Tag: 1757551579-987650 X-HE-Meta: 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 BPV5LHJd Os+Szzgok1bfxMRB5AyNeC+Wqhb4WwAjeA5xe6cVcGMniBoWxJmy0yH/FXKPfh8yQhZiU X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Jinchao, On Wed, 10 Sep 2025 13:23:10 +0800 Jinchao Wang 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 > --- > 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)