linux-kernel - Re: [PATCH v9 13/19] KVM: selftests: TDX: Use KVM_TDX_CAPABILITIES to validate TDs' attribute configuration

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Message-ID: <CAAhR5DFb1063E_zOLf8af_v3tQxx06cHtGL26j5XtojRv2GvLg@mail.gmail.com>
Date: Wed, 3 Sep 2025 22:57:19 -0500
From: Sagi Shahar <sagis@...gle.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: linux-kselftest@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, Sean Christopherson <seanjc@...gle.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Ryan Afranji <afranji@...gle.com>, 
	Andrew Jones <ajones@...tanamicro.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Erdem Aktas <erdemaktas@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Roger Wang <runanwang@...gle.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	"Pratik R. Sampat" <pratikrajesh.sampat@....com>, Reinette Chatre <reinette.chatre@...el.com>, 
	Ira Weiny <ira.weiny@...el.com>, Chao Gao <chao.gao@...el.com>, 
	Chenyi Qiang <chenyi.qiang@...el.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v9 13/19] KVM: selftests: TDX: Use KVM_TDX_CAPABILITIES to
 validate TDs' attribute configuration

On Tue, Aug 26, 2025 at 4:22 AM Binbin Wu <binbin.wu@...ux.intel.com> wrote:
>
>
>
> On 8/21/2025 12:29 PM, Sagi Shahar wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> >
> > This also exercises the KVM_TDX_CAPABILITIES ioctl.
>
> That commit message should describe what the patch does instead of relying on
> the title/short log.
>
> >
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > Co-developed-by: Sagi Shahar <sagis@...gle.com>
> > Signed-off-by: Sagi Shahar <sagis@...gle.com>
> > ---
> >   .../selftests/kvm/lib/x86/tdx/tdx_util.c        | 17 +++++++++++++++++
> >   1 file changed, 17 insertions(+)
> >
> > diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> > index 3869756a5641..d8eab99d9333 100644
> > --- a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> > +++ b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
> > @@ -232,6 +232,21 @@ static void vm_tdx_filter_cpuid(struct kvm_vm *vm,
> >       free(tdx_cap);
> >   }
> >
> > +static void tdx_check_attributes(struct kvm_vm *vm, uint64_t attributes)
> > +{
> > +     struct kvm_tdx_capabilities *tdx_cap;
> > +
> > +     tdx_cap = tdx_read_capabilities(vm);
> > +
> > +     /* TDX spec: any bits 0 in supported_attrs must be 0 in attributes */
> > +     TEST_ASSERT_EQ(attributes & ~tdx_cap->supported_attrs, 0);
> > +
> > +     /* TDX spec: any bits 1 in attributes must be 1 in supported_attrs */
>
> The comments are not accurate.
>
> The descriptions in TDX spec are for ATTRIBUTES_ FIXED0 and ATTRIBUTES_ FIXED1.
> They are related to tdx_cap->supported_attrs returned by KVM, but they are not
> the same.
>

I actually think that one of the conditions is redundant. Here's my reasoning:
If a bit is 0 in attributes then both conditions will be true
regardless of the value of supported_attrs.
If a bit is 1 in attributes then both conditions will be true iff the
corresponding bit in supported_attrs is 1.

I'm going to keep only the second condition which is clearer and
update the comment.

>
> > +     TEST_ASSERT_EQ(attributes & tdx_cap->supported_attrs, attributes);
> > +
> > +     free(tdx_cap);
> > +}
> > +
> >   void vm_tdx_init_vm(struct kvm_vm *vm, uint64_t attributes)
> >   {
> >       struct kvm_tdx_init_vm *init_vm;
> > @@ -251,6 +266,8 @@ void vm_tdx_init_vm(struct kvm_vm *vm, uint64_t attributes)
> >       memcpy(&init_vm->cpuid, cpuid, kvm_cpuid2_size(cpuid->nent));
> >       free(cpuid);
> >
> > +     tdx_check_attributes(vm, attributes);
> > +
> >       init_vm->attributes = attributes;
> >
> >       vm_tdx_vm_ioctl(vm, KVM_TDX_INIT_VM, 0, init_vm);
>