Re: [PATCH 1/2] KVM: VMX: Drop obsolete branch hint prefixes from inline asm

[Andrew Cooper]

> Remove explicit branch hint prefixes (.byte 0x2e / 0x3e) from VMX
> inline assembly sequences.
>
> These prefixes (CS/DS segment overrides used as branch hints on
> very old x86 CPUs) have been ignored by modern processors for a
> long time. Keeping them provides no measurable benefit and only
> enlarges the generated code.

It's actually worse than this.

The branch-taken hint has new meaning in Lion Cove cores and later,
along with a warning saying "performance penalty for misuse".

i.e. "only insert this prefix after profiling".

~Andrew