Re: [PATCH] PCI: brcmstb: Reserve only the MSI vectors that are handed out

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Oct 13, 2026 at 05:47:49PM +0900, Han / 한상우Sangwoo wrote:
> Hi Bjorn, Thomas,
> 
> > > Good. Can you please retest with the updated patch?
> >
> > Sangwoo, any update on this?
> 
> Sorry for the silence.
> 
> I have not been able to retest yet. I have several work items on a
> tight schedule right now, and I am currently working on a different
> board for another project, so I cannot get to this at the moment.
> 
> For the KASAN slab-out-of-bounds report, I will follow up within
> October.
> 
> For the retest with the updated patch, I cannot give a date right now.
> I am sorry about that.

No worries, just wanted to make sure we didn't drop this.  I have a
note to follow up again later :)

> 2026년 10월 13일 (화) 오전 6:47, Bjorn Helgaas <helgaas@kernel.org>님이 작성:
> >
> > On Thu, Oct 01, 2026 at 09:29:27PM +0200, Thomas Gleixner wrote:
> > > On Mon, Sep 21 2026 at 18:05, Han / 한상우Sangwoo wrote:
> > > > I tested Thomas's patch on the same hardware setup with the 5-vector
> > > > MSI endpoint. The patch was applied as posted on top of 6.12.93
> > > > (rpi-6.12.y).
> > > >
> > > > With the patch applied:
> > > >
> > > > - The MSI base hwirq remained at 0x8 across 200 driver reload cycles.
> > > > - The driver got all 5 requested vectors on every cycle, with no
> > > > single-MSI fallback. Multiple Message Enable remained at 8.
> > > > - The brcmstb inner-domain mapping returned to baseline after each
> > > > unload/reload, with 12 mapped while the driver was loaded and 4 after
> > > > unload.
> > > > - A kprobe showed one allocation of 8 vectors followed by eight
> > > > single-vector frees, with nothing left over.
> > >
> > > 8 single vector frees?
> > >
> > > Seems I got something wrong there verus the bulk free. Updated patch
> > > below.
> > >
> > > > The MSI vector exhaustion issue I originally observed no longer
> > > > reproduces with the patch.
> > >
> > > Good. Can you please retest with the updated patch?
> >
> > Sangwoo, any update on this?
> >
> > I don't see this patch in linux-next (next-20261012), so I don't think
> > this will be fixed for v7.4 unless something moves it ahead.
> >
> > > > I also observed a KASAN report with managed affinity. Using a small
> > > > out-of-tree test module bound to the same endpoint and requesting 1..3
> > > > vectors with PCI_IRQ_MSI | PCI_IRQ_AFFINITY, a request for 3 vectors
> > > > resulted in:
> > > >
> > > > BUG: KASAN: slab-out-of-bounds in __irq_alloc_descs+0x158/0x460
> > > >
> > > > Requests for 5 and 7 vectors were capped to 4 on this 4-CPU system and
> > > > did not trigger the report. I have not checked this against the
> > > > unpatched kernel yet, so I cannot tell whether it is related to the
> > > > patch.
> > >
> > > Any updates on that? Also please provide the source for that test.
> > >
> > > Thanks,
> > >
> > >         tglx
> > > ---
> > > --- a/kernel/irq/irqdomain.c
> > > +++ b/kernel/irq/irqdomain.c
> > > @@ -1610,6 +1610,17 @@ static void irq_domain_free_irqs_hierarc
> > >       if (!domain->ops->free)
> > >               return;
> > >
> > > +     /*
> > > +      * MSI device domains are capable of bulk free.
> > > +      *
> > > +      * CHECKME: Are all MSI parent domains capable?
> > > +      */
> > > +     if (domain->flags & (IRQ_DOMAIN_FLAG_MSI_DEVICE | IRQ_DOMAIN_FLAG_MSI_PARENT)) {
> > > +             if (irq_domain_get_irq_data(domain, irq_base))
> > > +                     domain->ops->free(domain, irq_base, nr_irqs);
> > > +             return;
> > > +     }
> > > +
> > >       for (i = 0; i < nr_irqs; i++) {
> > >               if (irq_domain_get_irq_data(domain, irq_base + i))
> > >                       domain->ops->free(domain, irq_base + i, 1);
> > > --- a/kernel/irq/msi.c
> > > +++ b/kernel/irq/msi.c
> > > @@ -1333,20 +1333,28 @@ static int __msi_domain_alloc_irqs(struc
> > >
> > >               ops->set_desc(&arg, desc);
> > >
> > > -             virq = __irq_domain_alloc_irqs(domain, -1, desc->nvec_used,
> > > +             /* Make sure a MULTI-MSI allocation is power of two */
> > > +             unsigned int nvec_aligned = roundup_pow_of_two(desc->nvec_used);
> > > +
> > > +             virq = __irq_domain_alloc_irqs(domain, -1, nvec_aligned,
> > >                                              dev_to_node(dev), &arg, false,
> > >                                              desc->affinity);
> > >               if (virq < 0)
> > >                       return msi_handle_pci_fail(domain, desc, allocated);
> > >
> > > -             for (i = 0; i < desc->nvec_used; i++) {
> > > +             for (i = 0; i < nvec_aligned; i++) {
> > >                       irq_set_msi_desc_off(virq, i, desc);
> > >                       irq_debugfs_copy_devname(virq + i, dev);
> > >                       ret = msi_init_virq(domain, virq + i, vflags);
> > >                       if (ret)
> > >                               return ret;
> > >               }
> > > +
> > >               if (info->flags & MSI_FLAG_DEV_SYSFS) {
> > > +                     /*
> > > +                      * This only exposes desc->nvec_used and ignores the
> > > +                      * overallocated MULTI-MSI ones.
> > > +                      */
> > >                       ret = msi_sysfs_populate_desc(dev, desc);
> > >                       if (ret)
> > >                               return ret;
> > > @@ -1610,13 +1618,15 @@ static void __msi_domain_free_irqs(struc
> > >                       continue;
> > >
> > >               /* Make sure all interrupts are deactivated */
> > > -             for (i = 0; i < desc->nvec_used; i++) {
> > > +             unsigned int nvec_aligned = roundup_pow_of_two(desc->nvec_used);
> > > +
> > > +             for (i = 0; i < nvec_aligned; i++) {
> > >                       irqd = irq_domain_get_irq_data(domain, desc->irq + i);
> > >                       if (irqd && irqd_is_activated(irqd))
> > >                               irq_domain_deactivate_irq(irqd);
> > >               }
> > >
> > > -             irq_domain_free_irqs(desc->irq, desc->nvec_used);
> > > +             irq_domain_free_irqs(desc->irq, nvec_aligned);
> > >               if (info->flags & MSI_FLAG_DEV_SYSFS)
> > >                       msi_sysfs_remove_desc(dev, desc);
> > >               desc->irq = 0;