On Wed, Jan 2, 2019 at 11:25 AM Liran Alon <liran.alon@xxxxxxxxxx> wrote: > > Only 0 or all 1s can be written to IA32_MCG_CTL. > SDM specifies other values as undefined and/or implementation specific. > > However, some guest kernels write different values. > One such example is WinNT 4 SP6 which uses a value of 0xffffffff. > > Prefer to silently accept these writes to avoid an uncatched #GP in the guest. > We will define our implementation specific behaviour as any value other than 0 > to be treated as all 1s. > > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> > Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx> > --- > arch/x86/kvm/x86.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 02c8e095a239..a06e4e892a9d 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2287,9 +2287,21 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > if (!(mcg_cap & MCG_CTL_P) && > (data || !msr_info->host_initiated)) > return 1; > - if (data != 0 && data != ~(u64)0) > - return 1; > - vcpu->arch.mcg_ctl = data; > + /* > + * Only 0 or all 1s can be written to IA32_MCG_CTL. > + * SDM specifies other values as undefined and/or > + * implementation specific. > + * > + * However, some guest kernels write different values. > + * One such example is WinNT 4 SP6 which uses a value > + * of 0xffffffff. > + * > + * Prefer to silently accept these writes to avoid an > + * uncatched #GP in the guest. We will define our > + * implementation specific behaviour as any value > + * other than 0 to be treated as all 1s. > + */ Isn't an "implementation" essentially a "family, model, and stepping"? I don't think you can define your own implementation-specific behavior unless you have F/M/S different from any actual hardware produced by Intel. > + vcpu->arch.mcg_ctl = data ? ~(u64)0 : 0; > break; > default: > if (msr >= MSR_IA32_MC0_CTL && > -- > 2.16.1 >
