From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paul Mackerras <paulus@ozlabs.org>
Date: Tue, 26 Feb 2019 04:25:15 +0000
Subject: Re: [PATCH v2 04/16] KVM: PPC: Book3S HV: XIVE: add a control to initialize a source
Message-Id: <20190226042515.GB28015@blackberry>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20190222112840.25000-1-clg@kaod.org>
 <20190222112840.25000-5-clg@kaod.org>
 <20190225021012.GH7668@umbus.fritz.box>
In-Reply-To: <20190225021012.GH7668@umbus.fritz.box>
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To: David Gibson <david@gibson.dropbear.id.au>
Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, =?iso-8859-1?Q?C=E9dric?= Le Goater <clg@kaod.org>, linuxppc-dev@lists.ozlabs.org

On Mon, Feb 25, 2019 at 01:10:12PM +1100, David Gibson wrote:
> On Fri, Feb 22, 2019 at 12:28:28PM +0100, C=E9dric 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 =3D xive_native_alloc_irq();
> > +		if (state->ipi_number =3D 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=3D0x%x for irq=3D0x%lx\n", __func__,
> > +			 state->ipi_number, irq);
> > +	}
> > +
> > +	arch_spin_lock(&sb->lock);
>=20
> 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.