Re: [PATCH] x86/cpu: Enable STIBP if Automatic IBRS is enabled

On Thu, Jul 20, 2023 at 12:48 PM Kim Phillips kim.phillips@amd.com wrote:

Unlike Intel's Enhanced IBRS feature, AMD's Automatic IBRS does not provide protection to processes running at CPL3/user mode [1].

Explicitly enable STIBP to protect against cross-thread CPL3 branch target injections on systems with Automatic IBRS enabled.

Is there any performance penalty to enabling STIBP + AUTOIBRS, aside from the lost sharing? Or does this just effectively tag the branch prediction information with thread ID?