linux-kernel - Re: [PATCH v8 06/30] KVM: selftests: Add helper functions to create TDX VMs

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Message-ID: <aJ6Zb+k+UkiTyB8/@intel.com>
Date: Fri, 15 Aug 2025 10:20:31 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Sagi Shahar <sagis@...gle.com>, <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 06/30] KVM: selftests: Add helper functions to create
 TDX VMs

>> +static struct kvm_cpuid_entry2 *tdx_find_cpuid_config(struct kvm_tdx_capabilities *cap,
>> +						      uint32_t leaf, uint32_t sub_leaf)
>> +{
>> +	struct kvm_cpuid_entry2 *config;
>> +	uint32_t i;
>> +
>> +	for (i = 0; i < cap->cpuid.nent; i++) {
>> +		config = &cap->cpuid.entries[i];
>> +
>> +		if (config->function == leaf && config->index == sub_leaf)
>> +			return config;
>> +	}
>> +
>> +	return NULL;
>> +}
>> +
>> +#define XFEATURE_MASK_CET (XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)
>
>One guess on what my feedback would be.

Move this to tools/testing/selftests/kvm/include/x86/processor.h?

or this is dead code as CET virtualization has not been merged. But I think
in general adding a test case for a feature before KVM's support is merged
should be acceptable. e.g., KVM-unit-tests has CET tests for a long time.

That said, I agree with Rick that the entire tdx_apply_cpuid_restrictions() is
unnecessary, as the supported CPUIDs reported by KVM should be sane.

>
>> +static void tdx_apply_cpuid_restrictions(struct kvm_cpuid2 *cpuid_data)
>> +{
>> +	for (int i = 0; i < cpuid_data->nent; i++) {
>> +		struct kvm_cpuid_entry2 *e = &cpuid_data->entries[i];
>> +
>> +		if (e->function == 0xd && e->index == 0) {
>> +			/*
>> +			 * TDX module requires both XTILE_{CFG, DATA} to be set.
>> +			 * Both bits are required for AMX to be functional.
>> +			 */
>> +			if ((e->eax & XFEATURE_MASK_XTILE) !=
>> +			    XFEATURE_MASK_XTILE) {
>> +				e->eax &= ~XFEATURE_MASK_XTILE;
>> +			}
>> +		}
>> +		if (e->function == 0xd && e->index == 1) {
>> +			/*
>> +			 * TDX doesn't support LBR yet.
>> +			 * Disable bits from the XCR0 register.
>> +			 */
>> +			e->ecx &= ~XFEATURE_MASK_LBR;
>> +			/*
>> +			 * TDX modules requires both CET_{U, S} to be set even
>> +			 * if only one is supported.
>> +			 */
>> +			if (e->ecx & XFEATURE_MASK_CET)
>> +				e->ecx |= XFEATURE_MASK_CET;
>> +		}
>> +	}
>> +}