Subject: Re: [PATCH v2 04/16] KVM: PPC: Book3S HV: XIVE: add a control to initialize a source

From: Paul Mackerras <[email-masked]>
Date: Tue, 26 Feb 2019 15:25:15 +1100

On Mon, Feb 25, 2019 at 01:10:12PM +1100, David Gibson wrote:
> On Fri, Feb 22, 2019 at 12:28:28PM +0100, Cédric Le Goater wrote:
> > +	/*
> > +	 * If the source doesn't already have an IPI, allocate
> > +	 * one and get the corresponding data
> > +	 */
> > +	if (!state->ipi_number) {
> > +		state->ipi_number = xive_native_alloc_irq();
> > +		if (state->ipi_number == 0) {
> > +			pr_err("Failed to allocate IRQ !\n");
> > +			return -ENXIO;
> > +		}
> > +		xive_native_populate_irq_data(state->ipi_number,
> > +					      &state->ipi_data);
> > +		pr_debug("%s allocated hw_irq=0x%x for irq=0x%lx\n", __func__,
> > +			 state->ipi_number, irq);
> > +	}
> > +
> > +	arch_spin_lock(&sb->lock);
> 
> Why the direct call to arch_spin_lock() rather than just spin_lock()?

He's sharing data structures with the xics-on-xive code, and that code
has a real-mode variant, and in real mode we don't want to risk
invoking lockdep code.  Hence sb->lock is an arch_spinlock_t, and he
has to use arch_spin_lock() on it.

Paul.