On 05/07/2018 03:43, Eduardo Habkost wrote: > 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 <[email protected]> > [...] > > 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. > Hi Eduardo, Thanks for your review, will provide the mechanism in next version. Jingqi
> [1] https://lkml.org/lkml/2018/6/29/408 > > -- > Eduardo
