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. + */ + vcpu->arch.mcg_ctl = data ? ~(u64)0 : 0; break; default: if (msr >= MSR_IA32_MC0_CTL && -- 2.16.1
