On Wed, Feb 20, 2019 at 08:15:31PM +0000, Joao Martins wrote:
> Xen usually places its MSR at 0x4000000 or 0x4000200 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 HyperV's MSR
> (HV_X64_MSR_GUEST_OS_ID) which uses the same address.
Unconditionally servicing Hyper-V and KVM MSRs seems wrong, i.e. KVM
should only expose MSRs specific to a hypervisor if userspace has
configured CPUID to advertise support for said hypervisor. If we do the
same thing for Xen, then the common MSR code looks like:
if (kvm_advertise_kvm()) {
if (<handle kvm msr>)
return ...;
} else if (kvm_advertise_hyperv()) {
if (<handle hyperv msr>)
return ...;
} else if (kvm_advertise_xen()) {
if (<handle xen msrs>)
return ...;
}
<fall through to main switch statement>
Obviously assumes KVM only advertises itself as one hypervisor, and so
the ordering is arbitrary.
> 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@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 65e4559eef2f..47360a4b0d42 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2429,6 +2429,9 @@ 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:
> @@ -2644,8 +2647,6 @@ 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);
> if (!ignore_msrs) {
> --
> 2.11.0
>
