Re: [PATCH V3] PCI/MSI: Fix MSI hwirq truncation

[Vidya Sagar]

On 1/15/2024 3:31 PM, Thomas Gleixner wrote:
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>
> On Fri, Jan 12 2024 at 23:03, Vidya Sagar wrote:
> > On 1/12/2024 9:23 PM, Thomas Gleixner wrote:
> > > On Thu, Jan 11 2024 at 10:58, Vidya Sagar wrote:
> > > > So, cast the PCI domain number to 'irq_hw_number_t' before left shifting
> > > > it to calculate hwirq number.
> > >
> > > This still does not explain that this fixes it only on 64-bit platforms
> > > and why we don't care for 32-bit systems.
> > Agree that this fixes the issue only on 64-bit platforms. It doesn't
> > change the behavior on 32-bit platforms. My understanding is that the
> > issue surfaces only if there are too many PCIe controllers in the system
> > which usually is the case in modern server systems and it is arguable if
> > the server systems really run 32-bit kernels.
>
> Arguably people who do that can keep the pieces.
>
> > One way to fix it for both 32-bit and 64-bit systems is by changing the
> > type of 'hwirq' to u64. This may cause two memory reads in 32-bit
> > systems whenever 'hwirq' is accessed and that may intern cause some perf
> > impact?? Is this the way you think I should be handling it?
>
> No. Leave it as is. What I'm asking for is that it's properly documented
> in the changelog.
Sure. I'll add this extra information in the change log.

> Thanks,
>
>          tglx