2019-06-17 14:31+0800, Xiaoyao Li: > On 6/17/2019 11:32 AM, Xiaoyao Li wrote: > > On 6/16/2019 5:55 PM, Tao Xu wrote: > > > + if (vmx->msr_ia32_umwait_control != host_umwait_control) > > > + add_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL, > > > + vmx->msr_ia32_umwait_control, > > > + host_umwait_control, false); > > > > The bit 1 is reserved, at least, we need to do below to ensure not > > modifying the reserved bit: > > > > guest_val = (vmx->msr_ia32_umwait_control & ~BIT_ULL(1)) | > > (host_val & BIT_ULL(1)) > > > > I find a better solution to ensure reserved bit 1 not being modified in > vmx_set_msr() as below: > > if((data ^ umwait_control_cached) & BIT_ULL(1)) > return 1; We could just be checking if (data & BIT_ULL(1)) because the guest cannot change its visible reserved value and KVM currently initializes the value to 0. The arch/x86/kernel/cpu/umwait.c series assumes that the reserved bit is 0 (hopefully deliberately) and I would do the same in KVM as it simplifies the logic. (We don't have to even think about migrations between machines with a different reserved value and making it play nicely with possible future implementations of that bit.) Thanks.
