linux-kernel - Re: [PATCH v8 04/30] KVM: selftests: Add vCPU descriptor table initialization utility

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Message-ID: <aJo1kNCUzAe2TFAz@google.com>
Date: Mon, 11 Aug 2025 11:25:20 -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
Subject: Re: [PATCH v8 04/30] KVM: selftests: Add vCPU descriptor table
 initialization utility

On Thu, Aug 07, 2025, Sagi Shahar wrote:
> From: Ackerley Tng <ackerleytng@...gle.com>
> 
> Turn vCPU descriptor table initialization into a utility for use by tests
> needing finer control, for example for TDX TD creation.

NAK.  "needing finer control" is not a sufficient explanation for why _this_
patch is necessary.  There's also zero argument made throughout any of these
patches as to why this pattern:

	vm = td_create();
	td_initialize(vm, VM_MEM_SRC_ANONYMOUS, 0);
	vcpu = td_vcpu_add(vm, 0, guest_io_writes);
	td_finalize(vm);

is the best approach.  IMO it is NOT the best approach.  I would much rather we
structure things so that creating TDs can use APIs like this:

static inline struct kvm_vm *td_create_with_vcpus(uint32_t nr_vcpus,
						  void *guest_code,
						  struct kvm_vcpu *vcpus[])
{
	return __vm_create_with_vcpus(VM_SHAPE_TDX, nr_vcpus, 0, guest_code, vcpus);
}

instead of open coding an entirely different set of APIs for creating TDs, which
is not maintanable.