Re: [PATCH 1/4] x86/altcall: Check and optimise altcall targets

[Jan Beulich <jbeulich@suse.com>]

On 26.11.2021 22:22, Andrew Cooper wrote:
> @@ -279,6 +280,27 @@ static void init_or_livepatch _apply_alternatives(struct alt_instr *start,
>  
>                  if ( dest )
>                  {
> +                    /*
> +                     * When building for CET-IBT, all function pointer targets
> +                     * should have an endbr64 instruction.
> +                     *
> +                     * If this is not the case, leave a warning because
> +                     * something is wrong with the build.
> +                     *
> +                     * Otherwise, skip the endbr64 instruction.  This is a
> +                     * marginal perf improvement which saves on instruction
> +                     * decode bandwidth.
> +                     */
> +                    if ( IS_ENABLED(CONFIG_HAS_CC_CET_IBT) )
> +                    {
> +                        if ( is_endbr64(dest) )

I would have given my R-b, but I don't see where is_endbr64() is coming
from, and you don't list any prereqs here or in the cover letter. I'm
afraid I don't fancy going hunt for it in the many other pending patches.
Hence only on the assumption that the helper has got introduced before:
Reviewed-by: Jan Beulich <jbeulich@suse.com>

Jan