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

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Message-ID: <aJo3ww82Ln-PxgGL@google.com>
Date: Mon, 11 Aug 2025 11:34:43 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sagi Shahar <sagis@...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 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;
	}