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

Xiaoyao Li
2024-03-20T08:15:30Z

On 2/26/2024 4:25 PM, isaku.yamahata@intel.com 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

> + }
> +