On 01/10/2021 14:33, Jane Malalane wrote: > Currently, Linux probes for X86_BUG_NULL_SEL unconditionally which > makes it unsafe to migrate in a virtualised environment as the > properties across the migration pool might differ. > > Zen3 adds the NullSelectorClearsBase bit to indicate that loading > a NULL segment selector zeroes the base and limit fields, as well as > just attributes. Zen2 also has this behaviour but doesn't have the > NSCB bit. > > When virtualised, NSCB might be cleared for migration safety, > therefore we must not probe. Always honour the NSCB bit in this case, > as the hypervisor is expected to synthesize it in the Zen2 case. > > Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
