Re: [PATCH v5 2/8] x86/bugs: Allow spectre_v2=ibrs on x86 vendors other than Intel

[Borislav Petkov]

On Fri, Sep 18, 2026 at 06:01:55PM -0500, Kim Phillips wrote:
> SPEC_CTRL.IBRS is architectural and behaves on AMD just like it does on
> Intel, but the kernel offers spectre_v2=ibrs on Intel only: the option is
> rejected at parse time on other vendors, and MITIGATION_IBRS_ENTRY cannot
> even be built into an AMD-only kernel.
> 
> AMD's SNP BTB Isolation needs the kernel to toggle legacy IBRS in order to
> optimize the VM exit-to-re-entry path, and right now there is no way to ask
> for kernel IBRS on an AMD machine at all.

Same comments as to the other one: We need:

- a proper use case which is *actually* useful to users

- have it properly documented in Documentation/admin-guide/hw-vuln/ along with
  the potential impact so that people can make an *informed* decision whether
  they really want it

Without any justification for the added complexity to what already is
a maintenance nightmare, there's no point.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette