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 76bce832cade251d6818d4899055252697213683..40be21f7c359d5e6c3e861258d068bf8d0e00fb5 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3008,6 +3008,9 @@ 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:
@@ -3295,8 +3298,6 @@ 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;