Re: [PATCH v9 3/6] x86/sev: Disable CPU hotplug while SNP is active

[Borislav Petkov]

On Fri, Jun 26, 2026 at 03:59:34PM -0500, Kalra, Ashish wrote:
> It can be that simple, and flag-free, by following the SNP_EN state:

Maybe. But that doesn't mean that you should not clean things up first where
needed. But I'll do a proper review once the dust from patchsets flying around
settles.

> We also have to re-enable cpu hotplug on the init failure paths 
> (snp_prepare()'s online != present check, and the SNP_INIT_EX / DF_FLUSH failures in 
> __sev_snp_init_locked()), so a failed init leaves hotplug enabled, as it was before
> this support.

You could also block hotplug for the time being by grabbing cpus_read_lock().
And only when you know you are all clear to disable hotplug, then you can do
that in the end and drop the hotplug lock.

> The only extra case is a kexec target that boots with SNP_EN already set (legacy
> firmware -- on X86_SNP_SHUTDOWN firmware the full shutdown required before kexec
> clears SNP_EN, so the target re-inits normally). There snp_prepare() bails, so I
> do the disable once at boot in snp_rmptable_init() when SNP_EN is already set.
> That and the snp_prepare() disable can't both run -- SNP_EN is either already set
> at boot, or it gets programmed by snp_prepare().

Ok.

Thx.

-- 
Regards/Gruss,
    Boris.

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