Re: [PATCH] KVM: selftests: sync_regs_test: use KVM_SYNC_X86_VALID_FIELDS

[Piotr Zarycki <piotr.zarycki@gmail.com>]

On Mon, May 11, 2026 at 07:56:50AM -0700, Sean Christopherson wrote:
> On Mon, May 11, 2026, Piotr Zarycki wrote:
> > Use KVM_SYNC_X86_VALID_FIELDS instead of open-coding the same three
> > flags, ensuring the test stays in sync with any future additions.
> > 
> > Signed-off-by: Piotr Zarycki <piotr.zarycki@gmail.com>
> > ---
> >  tools/testing/selftests/kvm/x86/sync_regs_test.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/kvm/x86/sync_regs_test.c b/tools/testing/selftests/kvm/x86/sync_regs_test.c
> > index e0c52321f87c..8f9239f9d357 100644
> > --- a/tools/testing/selftests/kvm/x86/sync_regs_test.c
> > +++ b/tools/testing/selftests/kvm/x86/sync_regs_test.c
> > @@ -79,7 +79,7 @@ static void compare_vcpu_events(struct kvm_vcpu_events *left,
> >  {
> >  }
> >  
> > -#define TEST_SYNC_FIELDS   (KVM_SYNC_X86_REGS|KVM_SYNC_X86_SREGS|KVM_SYNC_X86_EVENTS)
> > +#define TEST_SYNC_FIELDS   KVM_SYNC_X86_VALID_FIELDS
> 
> Explicitly defining the set of fields to test is very deliberate.  (a) we want
> to detect ABI breakage, e.g. if KVM removes a valid field.  (b) if a field is
> added in the future, the test likely needs to be updated, i.e. would break if
> KVM extends KVM_SYNC_X86_VALID_FIELDS.  (c) KVM_SYNC_X86_VALID_FIELDS probably
> shouldn't be defined in a uapi header; for all intents and purposes it's a KVM-
> internal details.
> 
> >  #define INVALID_SYNC_FIELD 0x80000000
> >  
> >  /*
> > @@ -255,7 +255,6 @@ KVM_ONE_VCPU_TEST(sync_regs_test, req_and_verify_all_valid, guest_code)
> >  	struct kvm_regs regs;
> >  
> >  	/* Request and verify all valid register sets. */
> > -	/* TODO: BUILD TIME CHECK: TEST_ASSERT(KVM_SYNC_X86_NUM_FIELDS != 3); */
> >  	run->kvm_valid_regs = TEST_SYNC_FIELDS;
> >  	vcpu_run(vcpu);
> >  	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
> > -- 
> > 2.54.0
> > 

Thanks for the explanation. What's the preferred way to implement the build-time check mentioned in the TODO?