Re: [PATCH V2] PCI/MSI: Fix MSI hwirq truncation

[Vidya Sagar]

On 1/10/2024 3:42 PM, Thomas Gleixner wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, Jan 08 2024 at 17:35, Vidya Sagar wrote:
>
> > While calculating the hwirq number for an MSI interrupt, the higher
> > bits (i.e. from bit-5 onwards a.k.a domain_nr >= 32) of the PCI domain
> > number gets truncated because of the shifted value casting to u32. This
> > for example is resulting in same hwirq number for devices 0019:00:00.0
> > and 0039:00:00.0.
> >
> > So, cast the PCI domain number to u64 before left shifting it to
> > calculate hwirq number.
> >
> > Fixes: 3878eaefb89a ("PCI/MSI: Enhance core to support hierarchy irqdomain")
> > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > ---
> > V2:
> > * Added Fixes tag
> >
> >   drivers/pci/msi/irqdomain.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
> > index c8be056c248d..cfd84a899c82 100644
> > --- a/drivers/pci/msi/irqdomain.c
> > +++ b/drivers/pci/msi/irqdomain.c
> > @@ -61,7 +61,7 @@ static irq_hw_number_t pci_msi_domain_calc_hwirq(struct msi_desc *desc)
> >
> >        return (irq_hw_number_t)desc->msi_index |
> >                pci_dev_id(dev) << 11 |
> > -             (pci_domain_nr(dev->bus) & 0xFFFFFFFF) << 27;
> > +             ((irq_hw_number_t)(pci_domain_nr(dev->bus) & 0xFFFFFFFF)) << 27;
>
> This is not casting to u64. It's casting to unsigned long:
>
>    typedef unsigned long irq_hw_number_t;
>
> So this works only correctly on 64bit. On 32bit kernels unsigned long is
> still 32bit. It's probably arguable that the 32bit case is not a
> problem, but the changelog and the change do not match. This needs a
> proper explanation why we don't care about this on 32bit.
Agree that the change and the commit message do not match.
I'll update the commit message to use 'irq_hw_number_t' instead of u64.

Thanks,
Vidya Sagar

> Thanks,
>
>          tglx