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

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Message-ID: <20200414082556.nfdgec63kuqknpxc@kamzik.brq.redhat.com>
Date:   Tue, 14 Apr 2020 10:25:56 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Wainer dos Santos Moschetta <wainersm@...hat.com>,
        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 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

> 
> 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"
> > 
>