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Mon, 24 Feb 2020 16:13:22 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 611A930605A; Mon, 24 Feb 2020 17:11:24 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CA8522B9A66D8; Mon, 24 Feb 2020 17:13:18 +0100 (CET) Date: Mon, 24 Feb 2020 17:13:18 +0100 From: Peter Zijlstra To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, dan.carpenter@oracle.com, mhiramat@kernel.org, Will Deacon , Petr Mladek , Marc Zyngier Subject: Re: [PATCH v4 02/27] hardirq/nmi: Allow nested nmi_enter() Message-ID: <20200224161318.GG14897@hirez.programming.kicks-ass.net> References: <20200221133416.777099322@infradead.org> <20200221134215.149193474@infradead.org> <20200221222129.GB28251@lenoir> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200221222129.GB28251@lenoir> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 21, 2020 at 11:21:30PM +0100, Frederic Weisbecker wrote: > On Fri, Feb 21, 2020 at 02:34:18PM +0100, Peter Zijlstra wrote: > > Since there are already a number of sites (ARM64, PowerPC) that > > effectively nest nmi_enter(), lets make the primitive support this > > before adding even more. > > > > Signed-off-by: Peter Zijlstra (Intel) > > Reviewed-by: Petr Mladek > > Acked-by: Will Deacon > > Acked-by: Marc Zyngier > > --- > > arch/arm64/include/asm/hardirq.h | 4 ++-- > > arch/arm64/kernel/sdei.c | 14 ++------------ > > arch/arm64/kernel/traps.c | 8 ++------ > > arch/powerpc/kernel/traps.c | 22 ++++++---------------- > > include/linux/hardirq.h | 5 ++++- > > include/linux/preempt.h | 4 ++-- > > kernel/printk/printk_safe.c | 6 ++++-- > > 7 files changed, 22 insertions(+), 41 deletions(-) > > > > --- a/kernel/printk/printk_safe.c > > +++ b/kernel/printk/printk_safe.c > > @@ -296,12 +296,14 @@ static __printf(1, 0) int vprintk_nmi(co > > > > void notrace printk_nmi_enter(void) > > { > > - this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK); > > + if (!in_nmi()) > > + this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK); > > } > > > > void notrace printk_nmi_exit(void) > > { > > - this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK); > > + if (!in_nmi()) > > + this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK); > > } > > If the outermost NMI is interrupted while between printk_nmi_enter() > and preempt_count_add(), there is still a risk that we race and clear? Damn, true. That also means I need to fix the arm64 bits, and that's a little more tricky. Something like so perhaps.. hmm? --- --- a/arch/arm64/include/asm/hardirq.h +++ b/arch/arm64/include/asm/hardirq.h @@ -32,30 +32,52 @@ u64 smp_irq_stat_cpu(unsigned int cpu); struct nmi_ctx { u64 hcr; + unsigned int cnt; }; DECLARE_PER_CPU(struct nmi_ctx, nmi_contexts); -#define arch_nmi_enter() \ - do { \ - if (is_kernel_in_hyp_mode() && !in_nmi()) { \ - struct nmi_ctx *nmi_ctx = this_cpu_ptr(&nmi_contexts); \ - nmi_ctx->hcr = read_sysreg(hcr_el2); \ - if (!(nmi_ctx->hcr & HCR_TGE)) { \ - write_sysreg(nmi_ctx->hcr | HCR_TGE, hcr_el2); \ - isb(); \ - } \ - } \ - } while (0) +#define arch_nmi_enter() \ +do { \ + struct nmi_ctx *___ctx; \ + unsigned int ___cnt; \ + \ + if (!is_kernel_in_hyp_mode() || in_nmi()) \ + break; \ + \ + ___ctx = this_cpu_ptr(&nmi_contexts); \ + ___cnt = ___ctx->cnt; \ + if (!(___cnt & 1) && __cnt) { \ + ___ctx->cnt += 2; \ + break; \ + } \ + \ + ___ctx->cnt |= 1; \ + barrier(); \ + nmi_ctx->hcr = read_sysreg(hcr_el2); \ + if (!(nmi_ctx->hcr & HCR_TGE)) { \ + write_sysreg(nmi_ctx->hcr | HCR_TGE, hcr_el2); \ + isb(); \ + } \ + barrier(); \ + if (!(___cnt & 1)) \ + ___ctx->cnt++; \ +} while (0) -#define arch_nmi_exit() \ - do { \ - if (is_kernel_in_hyp_mode() && !in_nmi()) { \ - struct nmi_ctx *nmi_ctx = this_cpu_ptr(&nmi_contexts); \ - if (!(nmi_ctx->hcr & HCR_TGE)) \ - write_sysreg(nmi_ctx->hcr, hcr_el2); \ - } \ - } while (0) +#define arch_nmi_exit() \ +do { \ + struct nmi_ctx *___ctx; \ + \ + if (!is_kernel_in_hyp_mode() || in_nmi()) \ + break; \ + \ + ___ctx = this_cpu_ptr(&nmi_contexts); \ + if ((___ctx->cnt & 1) || (___ctx->cnt -= 2)) \ + break; \ + \ + if (!(nmi_ctx->hcr & HCR_TGE)) \ + write_sysreg(nmi_ctx->hcr, hcr_el2); \ +} while (0) static inline void ack_bad_irq(unsigned int irq) {