On 18.12.2023 14:46, Jan Beulich wrote: > On 18.12.2023 13:11, Roger Pau Monné wrote: >> Hello, >> >> I'm not as expert as Andrew in all the speculation stuff, but I will >> try to provide some feedback. >> >> On Tue, Feb 14, 2023 at 05:10:42PM +0100, Jan Beulich wrote: >>> In order to be able to defer the context switch IBPB to the last >>> possible point, add logic to the exit-to-guest paths to issue the >>> barrier there, including the "IBPB doesn't flush the RSB/RAS" >>> workaround. Since alternatives, for now at least, can't nest, emit JMP >>> to skip past both constructs where both are needed. This may be more >>> efficient anyway, as the sequence of NOPs is pretty long. >> >> Could you elaborate on the reason why deferring the IBPB to the exit >> to guest path is helpful? So far it just seem to make the logic more >> complex without nay justification (at least in the changelog). > > I've added "(to leave behind as little as possible)" ahead of the 1st > comma - is that sufficient, do you think?
Actually, the next patch supplies better context, i.e. is more / also about avoiding to clobber Xen's own predictions. Jan
