Re: [PATCH v19 039/130] KVM: TDX: initialize VM with TDX specific parameters

[Xiaoyao Li]

On 2/26/2024 4:25 PM, isaku.yamahata@xxxxxxxxx wrote:

..

> +static int setup_tdparams_xfam(struct kvm_cpuid2 *cpuid, struct td_params *td_params)
> +{
> +	const struct kvm_cpuid_entry2 *entry;
> +	u64 guest_supported_xcr0;
> +	u64 guest_supported_xss;
> +
> +	/* Setup td_params.xfam */
> +	entry = kvm_find_cpuid_entry2(cpuid->entries, cpuid->nent, 0xd, 0);
> +	if (entry)
> +		guest_supported_xcr0 = (entry->eax | ((u64)entry->edx << 32));
> +	else
> +		guest_supported_xcr0 = 0;
> +	guest_supported_xcr0 &= kvm_caps.supported_xcr0;
> +
> +	entry = kvm_find_cpuid_entry2(cpuid->entries, cpuid->nent, 0xd, 1);
> +	if (entry)
> +		guest_supported_xss = (entry->ecx | ((u64)entry->edx << 32));
> +	else
> +		guest_supported_xss = 0;
> +
> +	/*
> +	 * PT and CET can be exposed to TD guest regardless of KVM's XSS, PT
> +	 * and, CET support.
> +	 */
> +	guest_supported_xss &=
> +		(kvm_caps.supported_xss | XFEATURE_MASK_PT | TDX_TD_XFAM_CET);
> +
> +	td_params->xfam = guest_supported_xcr0 | guest_supported_xss;
> +	if (td_params->xfam & XFEATURE_MASK_LBR) {
> +		/*
> +		 * TODO: once KVM supports LBR(save/restore LBR related
> +		 * registers around TDENTER), remove this guard.
> +		 */
> +#define MSG_LBR	"TD doesn't support LBR yet. KVM needs to save/restore IA32_LBR_DEPTH properly.\n"
> +		pr_warn(MSG_LBR);
> +		return -EOPNOTSUPP;

This unsupported behavior is totally decided by KVM even if TDX module 
supports it. I think we need to reflect it in tdx_info->xfam_fixed0, 
which gets reported to userspace via KVM_TDX_CAPABILITIES. So userspace 
will aware that LBR is not supported for TDs.

> +	}
> +
> +	return 0;
> +}
> +
> +static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
> +			struct kvm_tdx_init_vm *init_vm)
> +{
> +	struct kvm_cpuid2 *cpuid = &init_vm->cpuid;
> +	int ret;
> +
> +	if (kvm->created_vcpus)
> +		return -EBUSY;
> +
> +	if (init_vm->attributes & TDX_TD_ATTRIBUTE_PERFMON) {
> +		/*
> +		 * TODO: save/restore PMU related registers around TDENTER.
> +		 * Once it's done, remove this guard.
> +		 */
> +#define MSG_PERFMON	"TD doesn't support perfmon yet. KVM needs to save/restore host perf registers properly.\n"
> +		pr_warn(MSG_PERFMON);
> +		return -EOPNOTSUPP;

similar as above, we need reflect it in tdx_info->attributes_fixed0

> +	}
> +