Re: [PATCH 03/23] x86/srso: Don't probe microcode in a guest

[Andrew Cooper]

On 25/08/2023 8:01 am, Josh Poimboeuf wrote:
> To support live migration, the hypervisor sets the "lowest common
> denominator" of features.  Probing the microcode isn't allowed because
> any detected features might go away after a migration.
>
> As Andy Cooper states:
>
>   "Linux must not probe microcode when virtualised.  What it may see
>   instantaneously on boot (owing to MSR_PRED_CMD being fully passed
>   through) is not accurate for the lifetime of the VM."
>
> Rely on the hypervisor to set the needed IBPB_BRTYPE and SBPB bits.
>
> Fixes: 1b5277c0ea0b ("x86/srso: Add SRSO_NO support")
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Thankyou for doing this patch.