Re: [PATCH v3 hci-8.0/hci-8.1 3/6] i386: keep spec-ctrl for AMD guests on vz machine types up to vz9.2.0 #VSTOR-151770

[no-reply@sashiko.virtuozzo.com]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] i386: shared tsx_compat comment does not describe conditional spec_ctrl_compat
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commit f0225ca6e631cf113e6cd09a3b55911125b7a154
Author: Denis V. Lunev <den@openvz.org>

i386: keep spec-ctrl for AMD guests on vz machine types up to vz9.2.0 #VSTOR-151770

This patch adds an x-spec-ctrl-compat CPU property and enables it in
pc_vz_9_2_compat. On AMD guests, a requested spec-ctrl bit is kept when the
guest and host both report amd-ibpb and at least one of amd-ibrs, amd-stibp
or amd-ssbd.

> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 85efd0b9fbe5..740fb3aedc56 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -2337,6 +2337,7 @@ struct ArchCPU {
>       * older node keeps its CPUID.
>       */
>      bool tsx_compat;
> +    bool spec_ctrl_compat;
>  

[Severity: Low]
This isn't a bug, but the comment above tsx_compat now also appears to
cover spec_ctrl_compat:

    /*
     * Virtuozzo machine types up to vz9.2.0: do not filter requested
     * features the host no longer provides, so that a guest started on an
     * older node keeps its CPUID.
     */
    bool tsx_compat;
    bool spec_ctrl_compat;

Is that description accurate for the new flag? In
x86_cpu_compat_kept_features(), spec_ctrl_compat keeps SPEC_CTRL only when
the vendor is AMD, the guest and the host both have amd-ibpb, and at least
one of amd-ibrs, amd-stibp or amd-ssbd is present. It does not keep every
requested feature the host no longer provides.

Could spec_ctrl_compat get its own comment that describes these conditions?

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Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261029122527.365104-1-den@openvz.org?part=3