On Wed, Jul 04, 2018 at 09:21:06PM +0800, Jingqi Liu wrote: > The MSR (33H) controls support for #AC exception > for split locked accesses. When bit 29 of the MSR (33H) > is set, the processor causes an #AC exception to > be issued instead of suppressing LOCK on bus > (during split lock access). > > Signed-off-by: Jingqi Liu <jingqi....@intel.com> [...] > diff --git a/target/i386/machine.c b/target/i386/machine.c > index 4d98d36..c82dc0d 100644 > --- a/target/i386/machine.c > +++ b/target/i386/machine.c > @@ -935,6 +935,25 @@ static const VMStateDescription vmstate_msr_virt_ssbd = { > } > }; > > +static bool split_lock_ctrl_needed(void *opaque) > +{ > + X86CPU *cpu = opaque; > + CPUX86State *env = &cpu->env; > + > + return env->split_lock_ctrl != 0; > +}
Based on the Linux patch at [1], guests may try to detect the feature by writing to the MSR unconditionally. If this happens, KVM needs to provide a mechanism to enable/disable the MSR emulation. Otherwise users will end up with VMs that can't be migrated to older hosts even if they are using older machine-types. [1] https://lkml.org/lkml/2018/6/29/408 -- Eduardo