KVM: x86/xen: fix Xen hypercall page msr handling

Xen usually places its MSR at 0x40000000 or 0x40000200 depending on
whether it is running in viridian mode or not. Note that this is not
ABI guaranteed, so it is possible for Xen to advertise the MSR some
place else.

Given the way xen_hvm_config() is handled, if the former address is
selected, this will conflict with Hyper-V's MSR
(HV_X64_MSR_GUEST_OS_ID) which unconditionally uses the same address.

Given that the MSR location is arbitrary, move the xen_hvm_config()
handling to the top of kvm_set_msr_common() before falling through.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a480804ae27a3e3aa2bf6044262d96007e009b2f..c0c3a904080f03fb9e3b26a0eb5bebc9fe0245ed 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3007,6 +3007,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
        u32 msr = msr_info->index;
        u64 data = msr_info->data;
 
+       if (msr && msr == vcpu->kvm->arch.xen_hvm_config.msr)
+               return xen_hvm_config(vcpu, data);
+
        switch (msr) {
        case MSR_AMD64_NB_CFG:
        case MSR_IA32_UCODE_WRITE:
@@ -3294,8 +3297,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                vcpu->arch.msr_misc_features_enables = data;
                break;
        default:
-               if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
-                       return xen_hvm_config(vcpu, data);
                if (kvm_pmu_is_valid_msr(vcpu, msr))
                        return kvm_pmu_set_msr(vcpu, msr_info);
                return KVM_MSR_RET_INVALID;