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

[Jason Andryuk <jason.andryuk@amd.com>]

On 2026-06-24 11:59, Borislav Petkov wrote:
> + Andy
> 
> On Wed, Jun 24, 2026 at 11:41:16AM -0400, Jason Andryuk wrote:
>> I have wip s0ix support with Xen where dom0 issues the amd-pmc calls to
>> enter s0ix.  I'm not sure of all the uses of SMN, but with Xen dom0/hardware
>> domain running most drivers, I think it should be available.
> 
> Well, how should we make it available if dom0 doesn't really allow us to
> enumerate PCI roots and thus count AMD nodes?

dom0 enumerates the physical PCI roots.  It's just the dom0 vCPUs and 
topology are synthetic.

> Andy, see upthread.
> 
> What would you suggest we do here on dom0? We're trying to enumerate AMD
> nodes but dom0 is doing something special wrt topology and PCI roots - see
> get_next_root() in amd_node.c.
> 
> Thx.
> 

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.

We don't want dom0 to access the "CPU/node" devices.  It's the "root" 
device SMN access I am trying to retain.  Many amd_smn_read/write calls 
have hardcoded node 0, like for amd-pmc.

Regards,
Jason