Date:   Mon, 20 Mar 2023 16:36:30 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Xin Li <xin3.li@intel.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com,
        andrew.cooper3@citrix.com, seanjc@google.com, pbonzini@redhat.com,
        ravi.v.shankar@intel.com
Subject: Re: [PATCH v5 04/34] x86/traps: add external_interrupt() to dispatch
 external interrupts
Message-ID: <20230320153630.GO2194297@hirez.programming.kicks-ass.net>
References: <20230307023946.14516-1-xin3.li@intel.com>
 <20230307023946.14516-5-xin3.li@intel.com>
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On Mon, Mar 06, 2023 at 06:39:16PM -0800, Xin Li wrote:

> +#ifndef CONFIG_X86_LOCAL_APIC
> +/*
> + * Used when local APIC is not compiled into the kernel, but
> + * external_interrupt() needs dispatch_spurious_interrupt().
> + */
> +DEFINE_IDTENTRY_IRQ(spurious_interrupt)
> +{
> +	pr_info("Spurious interrupt (vector 0x%x) on CPU#%d, should never happen.\n",
> +		vector, smp_processor_id());
> +}
> +#endif
> +
> +/*
> + * External interrupt dispatch function.
> + *
> + * Until/unless dispatch_common_interrupt() can be taught to deal with the
> + * special system vectors, split the dispatch.
> + *
> + * Note: dispatch_common_interrupt() already deals with IRQ_MOVE_CLEANUP_VECTOR.
> + */
> +int external_interrupt(struct pt_regs *regs, unsigned int vector)
> +{
> +	unsigned int sysvec = vector - FIRST_SYSTEM_VECTOR;
> +
> +	if (vector < FIRST_EXTERNAL_VECTOR) {
> +		pr_err("invalid external interrupt vector %d\n", vector);
> +		return -EINVAL;
> +	}
> +
> +	if (sysvec < NR_SYSTEM_VECTORS) {
> +		if (system_interrupt_handlers[sysvec])
> +			system_interrupt_handlers[sysvec](regs);
> +		else
> +			dispatch_spurious_interrupt(regs, vector);

ISTR suggesting you can get rid of this branch if you stuff
system_interrupt_handlers[] with dispatch_spurious_interrupt instead of
NULL.

> +	} else {
> +		dispatch_common_interrupt(regs, vector);
> +	}
> +
> +	return 0;
> +}