Re: [RFC PATCH 1/4] KVM: selftests: Add support for creating non-default type VMs

Sean Christopherson
2021-07-27T20:47:52Z

On Mon, Jul 26, 2021, David Matlack wrote:
> On Mon, Jul 26, 2021 at 11:37:54AM -0700, Erdem Aktas wrote:
> > Currently vm_create function only creates KVM_X86_LEGACY_VM type VMs.
> > Changing the vm_create function to accept type parameter to create
> > new VM types.
> >
> > Signed-off-by: Erdem Aktas <erdemaktas@google.com>
> > Reviewed-by: Sean Christopherson <seanjc@google.com>

*-by tags should not be added unless explicitly provided. IIRC, our internal
gerrit will convert +1 to Reviewed-by, but I don't think that's the case here.
This applies to all patches in this series.

See "Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:" in
Documentation/process/submitting-patches.rst for more info.

> > Reviewed-by: Peter Gonda <pgonda@google.com>
> > Reviewed-by: Marc Orr <marcorr@google.com>
> > Reviewed-by: Sagi Shahar <sagis@google.com>
>
> Reviewed-by: David Matlack <dmatlack@google.com>
>
> (aside from the nit below)
>
> > ---
> > .../testing/selftests/kvm/include/kvm_util.h | 1 +
> > tools/testing/selftests/kvm/lib/kvm_util.c | 29 +++++++++++++++++--
> > 2 files changed, 27 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> > index d53bfadd2..c63df42d6 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> > @@ -88,6 +88,7 @@ int vcpu_enable_cap(struct kvm_vm *vm, uint32_t vcpu_id,
> > void vm_enable_dirty_ring(struct kvm_vm *vm, uint32_t ring_size);
> >
> > struct kvm_vm *vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm);
> > +struct kvm_vm *__vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm, int type);
>
> nit: Consider using a more readable function name such as
> vm_create_with_type().

Ha! This is why I don't like doing internal reviews :-D

Erdem originally had vm_create_type(), I suggested __vm_create() as the double
underscore scheme is more common in the kernel for cases where there's a default
wrapper and an inner helper that implements the full API.

Convention aside, the argument againsts ...with_type() are that it doesn't scale,
e.g. if someone adds another parameter parameter for which vm_create() provides a
default, and it doesn't self-document the relationship between vm_create() and
the inner helper, e.g. by convention, based on names alone I know that vm_create()
likely is a wrapper around __vm_create().

Compare that with the existing

vm_create_default_with_vcpus()
vm_create_default()
vm_create_with_vcpus()
vm_create()

where the relationship between all the helpers is not immediately clear, and
vm_create_with_vcpus() is a misnomer because it does much more than call vm_create()
and instantiate vCPUs, e.g. it also instantiates the IRQ chip and loads the test
into guest memory.