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Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-perf-users@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 05/18] x86/hw_breakpoint: introduce arch_reinstall_hw_breakpoint() for atomic context Message-ID: <20250904063832.GT4067720@noisy.programming.kicks-ass.net> References: <20250904002126.1514566-1-wangjinchao600@gmail.com> <20250904002126.1514566-6-wangjinchao600@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250904002126.1514566-6-wangjinchao600@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 69B5D40007 X-Stat-Signature: bbpq1zkbsm5diwa1diugq39jatg53dm9 X-HE-Tag: 1756967921-238344 X-HE-Meta: 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 53JT9gqT NOpRuNN+jkmpZnmI6KB9fE58N73zb/n9+E2xdS10XoOlQf0fxNCCj1QpP9EVc6QA68gdCJBo06MqIcQIjnYemXS2GeJkL/13rO3DaxdC+jDoYimYWe8aFBA8uZ2TJAV+bZcZaB1HNZMj9I3oTCIEc8fZGwpBwXIGR2PQcY8Mvftf+AfE7Jr/UfDCfXtQLfbcBJv6cBPSbrX+SIyKlcHyl9eu2cw== 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: On Thu, Sep 04, 2025 at 08:21:02AM +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); Yeah, I think not. For one this is an almost verbatim copy of arch_install_hw_breakpoint() with zero re-use. Surely you've been taught better? And why would we want to export guts like this?