linux-kernel - Re: [PATCH 01/10] KVM: selftests: Take vcpu pointer instead of id in vm_vcpu

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Date:   Tue, 14 Apr 2020 10:02:08 -0300
From:   Wainer dos Santos Moschetta <wainersm@...hat.com>
To:     Andrew Jones <drjones@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 01/10] KVM: selftests: Take vcpu pointer instead of id in
 vm_vcpu_rm()


On 4/14/20 5:25 AM, Andrew Jones wrote:
> On Mon, Apr 13, 2020 at 02:26:59PM -0700, Sean Christopherson wrote:
>> On Mon, Apr 13, 2020 at 03:26:55PM -0300, Wainer dos Santos Moschetta wrote:
>>> On 4/10/20 8:16 PM, Sean Christopherson wrote:
>>>> The sole caller of vm_vcpu_rm() already has the vcpu pointer, take it
>>>> directly instead of doing an extra lookup.
>>>
>>> Most of (if not all) vcpu related functions in kvm_util.c receives an id, so
>>> this change creates an inconsistency.
>> Ya, but taking the id is done out of "necessity", as everything is public
>> and for whatever reason the design of the selftest framework is to not
>> expose 'struct vcpu' outside of the utils.  vm_vcpu_rm() is internal only,
>> IMO pulling the id out of the vcpu just to lookup the same vcpu is a waste
>> of time.
> Agreed


Thanks Sean and Andrew for your comments. I'm not in position to 
change/propose any design of kvm selftests but even though I aimed to 
foster this discussion.

So, please, consider my Reviewed-by...

- Wainer


>
>> FWIW, I think the whole vcpuid thing is a bad interface, almost all the
>> tests end up defining an arbitrary number for the sole VCPU_ID, i.e. the
>> vcpuid interface just adds a pointless layer of obfuscation.  I haven't
>> looked through all the tests, but returning the vcpu and making the struct
>> opaque, same as kvm_vm, seems like it would yield more readable code with
>> less overhead.
> Agreed
>
>> While I'm on a soapbox, hiding 'struct vcpu' and 'struct kvm_vm' also seems
>> rather silly, but at least that doesn't directly lead to funky code.
> Agreed. While the concept has been slowly growing on me, I think accessor
> functions for each of the structs members are growing even faster...
>
> Thanks,
> drew
>
>>> Disregarding the above comment, the changes look good to me. So:
>>>
>>> Reviewed-by: Wainer dos Santos Moschetta <wainersm@...hat.com>
>>>
>>>
>>>> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
>>>> ---
>>>>   tools/testing/selftests/kvm/lib/kvm_util.c | 7 +++----
>>>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
>>>> index 8a3523d4434f..9a783c20dd26 100644
>>>> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
>>>> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
>>>> @@ -393,7 +393,7 @@ struct vcpu *vcpu_find(struct kvm_vm *vm, uint32_t vcpuid)
>>>>    *
>>>>    * Input Args:
>>>>    *   vm - Virtual Machine
>>>> - *   vcpuid - VCPU ID
>>>> + *   vcpu - VCPU to remove
>>>>    *
>>>>    * Output Args: None
>>>>    *
>>>> @@ -401,9 +401,8 @@ struct vcpu *vcpu_find(struct kvm_vm *vm, uint32_t vcpuid)
>>>>    *
>>>>    * Within the VM specified by vm, removes the VCPU given by vcpuid.
>>>>    */
>>>> -static void vm_vcpu_rm(struct kvm_vm *vm, uint32_t vcpuid)
>>>> +static void vm_vcpu_rm(struct kvm_vm *vm, struct vcpu *vcpu)
>>>>   {
>>>> -	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
>>>>   	int ret;
>>>>   	ret = munmap(vcpu->state, sizeof(*vcpu->state));
>>>> @@ -427,7 +426,7 @@ void kvm_vm_release(struct kvm_vm *vmp)
>>>>   	int ret;
>>>>   	while (vmp->vcpu_head)
>>>> -		vm_vcpu_rm(vmp, vmp->vcpu_head->id);
>>>> +		vm_vcpu_rm(vmp, vmp->vcpu_head);
>>>>   	ret = close(vmp->fd);
>>>>   	TEST_ASSERT(ret == 0, "Close of vm fd failed,\n"