Re: [PATCH] KVM: nVMX: fixes for preemption timer migration

[Bandan Das <bsd@redhat.com>]

Jim Mattson <jmattson@google.com> writes:

> On Thu, Jul 9, 2020 at 10:15 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> Commit 850448f35aaf ("KVM: nVMX: Fix VMX preemption timer migration",
>> 2020-06-01) accidentally broke nVMX live migration from older version
>> by changing the userspace ABI.  Restore it and, while at it, ensure
>> that vmx->nested.has_preemption_timer_deadline is always initialized
>> according to the KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE flag.
>>
>> Cc: Makarand Sonare <makarandsonare@google.com>
>> Fixes: 850448f35aaf ("KVM: nVMX: Fix VMX preemption timer migration")
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  arch/x86/include/uapi/asm/kvm.h | 5 +++--
>>  arch/x86/kvm/vmx/nested.c       | 3 ++-
>>  2 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
>> index 17c5a038f42d..0780f97c1850 100644
>> --- a/arch/x86/include/uapi/asm/kvm.h
>> +++ b/arch/x86/include/uapi/asm/kvm.h
>> @@ -408,14 +408,15 @@ struct kvm_vmx_nested_state_data {
>>  };
>>
>>  struct kvm_vmx_nested_state_hdr {
>> -       __u32 flags;
>>         __u64 vmxon_pa;
>>         __u64 vmcs12_pa;
>> -       __u64 preemption_timer_deadline;
>>
>>         struct {
>>                 __u16 flags;
>>         } smm;
>> +
>> +       __u32 flags;
>> +       __u64 preemption_timer_deadline;
>>  };
>>
Oops!

>>  struct kvm_svm_nested_state_data {
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index b26655104d4a..3fc2411edc92 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -6180,7 +6180,8 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
>>                 vmx->nested.has_preemption_timer_deadline = true;
>>                 vmx->nested.preemption_timer_deadline =
>>                         kvm_state->hdr.vmx.preemption_timer_deadline;
>> -       }
>> +       } else
>> +               vmx->nested.has_preemption_timer_deadline = false;
>
> Doesn't the coding standard require braces around the else clause?
>
I think so... for if/else where at least one of them is multiline.

> Reviewed-by: Jim Mattson <jmattson@google.com>

Looks good to me, 
Reviewed-by: Bandan Das <bsd@redhat.com>