linux-kernel - Re: [PATCH v8 05/30] KVM: selftests: Update kvm_init_vm_address

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Message-ID: <CAAhR5DF5RTT8nF6mwLQPePL01k-bXBLapZZ3uNLH01j1W4UjSQ@mail.gmail.com>
Date: Thu, 14 Aug 2025 23:31:55 -0500
From: Sagi Shahar <sagis@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kselftest@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, 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>, 
	Binbin Wu <binbin.wu@...ux.intel.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>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v8 05/30] KVM: selftests: Update kvm_init_vm_address_properties()
 for TDX

On Mon, Aug 11, 2025 at 1:34 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Thu, Aug 07, 2025, Sagi Shahar wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> >
> > Let kvm_init_vm_address_properties() initialize vm->arch.{s_bit, tag_mask}
> > similar to SEV.
> >
> > Set shared bit position based on guest maximum physical address width
> > instead of maximum physical address width, because that is what KVM
> > uses,
>
> "because KVM does it" is not an acceptable explanation.
>
> > refer to setup_tdparams_eptp_controls(), and because maximum physical
> > address width can be different.
> >
> > In the case of SRF, guest maximum physical address width is 48 because SRF
> > does not support 5-level EPT, even though the maximum physical address
> > width is 52.
>
> Referencing a specific Intel microarchitecture is not proper justification for
> why something is supported/legal/correct.  Using its three-letter acronym is
> just icing on the cake.
>
> > Co-developed-by: Adrian Hunter <adrian.hunter@...el.com>
> > Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > Signed-off-by: Sagi Shahar <sagis@...gle.com>
> > ---
> >  tools/testing/selftests/kvm/lib/x86/processor.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
> > index d082d429e127..5718b5911b0a 100644
> > --- a/tools/testing/selftests/kvm/lib/x86/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/x86/processor.c
> > @@ -1166,10 +1166,19 @@ void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits)
> >
> >  void kvm_init_vm_address_properties(struct kvm_vm *vm)
> >  {
> > +     uint32_t gpa_bits = kvm_cpu_property(X86_PROPERTY_GUEST_MAX_PHY_ADDR);
> > +
> >       if (is_sev_vm(vm)) {
> >               vm->arch.sev_fd = open_sev_dev_path_or_exit();
> >               vm->arch.c_bit = BIT_ULL(this_cpu_property(X86_PROPERTY_SEV_C_BIT));
> >               vm->gpa_tag_mask = vm->arch.c_bit;
> > +     } else if (vm->type == KVM_X86_TDX_VM) {
>
> Please add an is_tdx_vm() helper.
>
> > +             TEST_ASSERT(gpa_bits == 48 || gpa_bits == 52,
> > +                         "TDX: bad X86_PROPERTY_GUEST_MAX_PHY_ADDR value: %u", gpa_bits);
> > +             vm->arch.sev_fd = -1;
> > +             vm->arch.s_bit = 1ULL << (gpa_bits - 1);
> > +             vm->arch.c_bit = 0;
>
> The VM is zero-initialized, no need to set c_bit.
>
> > +             vm->gpa_tag_mask = vm->arch.s_bit;
> >       } else {
> >               vm->arch.sev_fd = -1;
>
> I think it makes sense to set sev_fd to -1 by default instead of duplicating the
> non-SEV logic into all non-SEV paths.  SEV VMs will write it twice, but that's a
> non-issue.  E.g.
>
>         vm->arch.sev_fd = -1;
>
>         if (is_sev_vm(vm)) {
>                 vm->arch.sev_fd = open_sev_dev_path_or_exit();
>                 vm->arch.c_bit = BIT_ULL(this_cpu_property(X86_PROPERTY_SEV_C_BIT));
>                 vm->gpa_tag_mask = vm->arch.c_bit;
>         } else if (is_tdx_vm(vm)) {
>                 TEST_ASSERT(gpa_bits == 48 || gpa_bits == 52,
>                             "TDX: bad X86_PROPERTY_GUEST_MAX_PHY_ADDR value: %u", gpa_bits);
>                 vm->arch.s_bit = 1ULL << (gpa_bits - 1);
>                 vm->gpa_tag_mask = vm->arch.s_bit;
>         }
>

Thanks for all the suggestions. I will incorporate them in the next version.