On Fri, Nov 4, 2022 at 2:38 PM Kim Phillips <kim.phillips@xxxxxxx> wrote: > > VM Guests may want to use Auto IBRS, so propagate the CPUID to them. > > Co-developed-by: Babu Moger <Babu.Moger@xxxxxxx> > Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx> The APM says that, under AutoIBRS, CPL0 processes "have IBRS protection." I'm taking this to mean only that indirect branches in CPL0 are not subject to steering from a less privileged predictor mode. This would imply that indirect branches executed at CPL0 in L1 could potentially be subject to steering by code running at CPL0 in L2, since L1 and L2 share hardware predictor modes. Fortunately, there is an IBPB when switching VMCBs in svm_vcpu_load(). But it might be worth noting that this is necessary for AutoIBRS to work (unless it actually isn't).
