linux-kernel - Re: [PATCH 05/10] iommu/amd: remove the special case from get_irq

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Date:   Thu, 15 Mar 2018 14:07:23 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de
Subject: Re: [PATCH 05/10] iommu/amd: remove the special case from
 get_irq_table()

On Thu, Mar 15, 2018 at 02:01:53PM +0100, Sebastian Andrzej Siewior wrote:
> On 2018-03-15 13:53:42 [+0100], Joerg Roedel wrote:
> > On Fri, Feb 23, 2018 at 11:27:31PM +0100, Sebastian Andrzej Siewior wrote:
> > > @@ -4103,10 +4093,26 @@ static int irq_remapping_alloc(struct irq_domain *domain, unsigned int virq,
> > >  		return ret;
> > >  
> > >  	if (info->type == X86_IRQ_ALLOC_TYPE_IOAPIC) {
> > > -		if (get_irq_table(devid, true))
> > > +		struct irq_remap_table *table;
> > > +		struct amd_iommu *iommu;
> > > +
> > > +		table = get_irq_table(devid);
> > > +		if (table) {
> > > +			if (!table->min_index) {
> > > +				/*
> > > +				 * Keep the first 32 indexes free for IOAPIC
> > > +				 * interrupts.
> > > +				 */
> > > +				table->min_index = 32;
> > > +				iommu = amd_iommu_rlookup_table[devid];
> > > +				for (i = 0; i < 32; ++i)
> > > +					iommu->irte_ops->set_allocated(table, i);
> > > +			}
> > 
> > I think this needs to be protected by the table->lock.
> 
> Which part any why? The !->min_index part plus extending(setting to 32)?

In particular the set_allocated part, when get_irq_table() returns the
table is visible to other users as well. I have not checked the
irq-layer locking to be sure that can happen, though.