Re: [PATCH 1/2] x86/amd_node: Remove smn_exclusive

[Borislav Petkov]

On Thu, Aug 13, 2026 at 09:40:33AM -0400, Jason Andryuk wrote:
> On 2026-08-12 15:28, Borislav Petkov wrote:
> > On Mon, Aug 10, 2026 at 10:07:47AM -0400, Yazen Ghannam wrote:
> > > 'smn_exclusive' wasn't originally intended to be used for bounds
> > > checking the array. But the original use is no longer needed, so it can
> > > be removed.
> > 
> > Why is it no longer needed? Apparently I didn't get that memo yet...
> > 
> > 83518453074d ("x86/amd_node: Add SMN offsets to exclusive region access") is
> > talking about the potential concurrent access. Why is that ok now all of
> > a sudden?
> 83518453074d set smn_exclusive after successfully calling
> pci_request_config_region_exclusive().  smn_exclusive gated access in
> __amd_smn_rw().
> 
> Things moved around, and now pci_request_config_region_exclusive() is called
> earlier.  At the end of amd_smn_init(), either amd_roots == NULL and
> smn_exclusive == false or amd_roots != NULL and smn_exclusive == true.
> smn_exclusive is redundant, and amd_roots can just be used directly.

So you want to use amd_roots to *also* *denote* whether exclusive SMN access
is enabled. Then you need to at least put a comment in __amd_smn_rw() where
you're testing it, what exactly that test means.

Then, your patch has a Fixes: tag and CC:stable which means, it needs to go to
all kernels but then I don't know what you're fixing.

Looking at it more, you're basically fixing one more aspect of running the
kernel as a Xen guest and it not having AMD roots exported.

But what you really wanna do, IMNSVHO, you want to make your patch 2 be patch
1 and it can go to stable.

Your patch 1 then becomes a simplification/cleanup patch which goes as patch
2 and doesn't need to be Cc:stable but it can be queued later, during the
normal cycle.

Right?

Anything I'm missing?

Thx.

-- 
Regards/Gruss,
    Boris.

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