Re: [PATCH] x86: Avoid divide by 0 in amd_smn_init()

[Jason Andryuk]

On 2026-06-24 13:15, Borislav Petkov wrote:
> On Wed, Jun 24, 2026 at 12:41:48PM -0400, Jason Andryuk wrote:
> > I think this is the issue:
> >
> >      The "root" device search was introduced to support SMN access for Zen
> >      systems. This device represents a PCIe root complex. It is not the
> >      same as the "CPU/node" devices found at slots 0x18-0x1F.
>
> What is that? AI output?

It's from the commit message of 40a5f6ffdfc8f8ed0d8c535dfa3733b31c66a88c

> > We don't want dom0 to access the "CPU/node" devices.  It's the "root" device
> > SMN access I am trying to retain.
>
> I know what you're trying to do - you want to use SMN accesses on dom0. And
> I'm trying to figure out a stable detection method on Xen which is future
> proof.
>
> > Many amd_smn_read/write calls have hardcoded node 0, like for amd-pmc.
>
> Maybe.
>
> Whatever it is, it needs to be a long-term solution and properly vetted by Xen
> folks so that we don't do crazy hacks for Xen's sake everytime.

Sure.

I think Ingo's suggestion to re-add the check will at least get systems 
booting again.  Then when Xen SMN accesses is sorted out, that can be 
changed as necessary.

Regards,
Jason