From: Vitaly Kuznetsov vkuznets@redhat.com

commit b1e34d325397a33d97d845e312d7cf2a8b646b44 upstream.

Setting non-zero values to SYNIC/STIMER MSRs activates certain features, this should not happen when KVM_CAP_HYPERV_SYNIC{,2} was not activated.

Note, it would've been better to forbid writing anything to SYNIC/STIMER MSRs, including zeroes, however, at least QEMU tries clearing HV_X64_MSR_STIMER0_CONFIG without SynIC. HV_X64_MSR_EOM MSR is somewhat 'special' as writing zero there triggers an action, this also should not happen when SynIC wasn't activated.

Signed-off-by: Vitaly Kuznetsov vkuznets@redhat.com Message-Id: 20220325132140.25650-4-vkuznets@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com --- arch/x86/kvm/hyperv.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 23ff65504d7e..cf2a8b086fcd 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -205,7 +205,7 @@ static int synic_set_msr(struct kvm_vcpu_hv_synic *synic, struct kvm_vcpu *vcpu = synic_to_vcpu(synic); int ret;

- if (!synic->active && !host) + if (!synic->active && (!host || data)) return 1;

trace_kvm_hv_synic_set_msr(vcpu->vcpu_id, msr, data, host); @@ -251,6 +251,9 @@ static int synic_set_msr(struct kvm_vcpu_hv_synic *synic, case HV_X64_MSR_EOM: { int i;

+ if (!synic->active) + break; + for (i = 0; i < ARRAY_SIZE(synic->sint); i++) kvm_hv_notify_acked_sint(vcpu, i); break; @@ -514,6 +517,11 @@ static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config, { union hv_stimer_config new_config = {.as_uint64 = config}, old_config = {.as_uint64 = stimer->config.as_uint64}; + struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer); + struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu); + + if (!synic->active && (!host || config)) + return 1;

trace_kvm_hv_stimer_set_config(stimer_to_vcpu(stimer)->vcpu_id, stimer->index, config, host); @@ -533,6 +541,12 @@ static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config, static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count, bool host) { + struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer); + struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu); + + if (!synic->active && (!host || count)) + return 1; + trace_kvm_hv_stimer_set_count(stimer_to_vcpu(stimer)->vcpu_id, stimer->index, count, host);