[bug report] KVM: TDX: Get system-wide info about TDX module on initialization

[bug report] KVM: TDX: Get system-wide info about TDX module on initialization

[Dan Carpenter]

Hello Isaku Yamahata,

Commit 61bb28279623 ("KVM: TDX: Get system-wide info about TDX module
on initialization") from Oct 30, 2024 (linux-next), leads to the
following Smatch static checker warning:

	arch/x86/kvm/vmx/tdx.c:3464 __tdx_bringup()
	warn: missing error code 'r'

arch/x86/kvm/vmx/tdx.c
    3416 static int __init __tdx_bringup(void)
    3417 {
    3418         const struct tdx_sys_info_td_conf *td_conf;
    3419         int r, i;
    3420 
    3421         for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
    3422                 /*
    3423                  * Check if MSRs (tdx_uret_msrs) can be saved/restored
    3424                  * before returning to user space.
    3425                  *
    3426                  * this_cpu_ptr(user_return_msrs)->registered isn't checked
    3427                  * because the registration is done at vcpu runtime by
    3428                  * tdx_user_return_msr_update_cache().
    3429                  */
    3430                 tdx_uret_msrs[i].slot = kvm_find_user_return_msr(tdx_uret_msrs[i].msr);
    3431                 if (tdx_uret_msrs[i].slot == -1) {
    3432                         /* If any MSR isn't supported, it is a KVM bug */
    3433                         pr_err("MSR %x isn't included by kvm_find_user_return_msr\n",
    3434                                 tdx_uret_msrs[i].msr);
    3435                         return -EIO;
    3436                 }
    3437         }
    3438 
    3439         /*
    3440          * Enabling TDX requires enabling hardware virtualization first,
    3441          * as making SEAMCALLs requires CPU being in post-VMXON state.
    3442          */
    3443         r = kvm_enable_virtualization();
    3444         if (r)
    3445                 return r;
    3446 
    3447         cpus_read_lock();
    3448         r = __do_tdx_bringup();
    3449         cpus_read_unlock();
    3450 
    3451         if (r)
    3452                 goto tdx_bringup_err;
    3453 
    3454         /* Get TDX global information for later use */
    3455         tdx_sysinfo = tdx_get_sysinfo();
    3456         if (WARN_ON_ONCE(!tdx_sysinfo)) {
    3457                 r = -EINVAL;
    3458                 goto get_sysinfo_err;
    3459         }
    3460 
    3461         /* Check TDX module and KVM capabilities */
    3462         if (!tdx_get_supported_attrs(&tdx_sysinfo->td_conf) ||
    3463             !tdx_get_supported_xfam(&tdx_sysinfo->td_conf))
--> 3464                 goto get_sysinfo_err;

error code?

    3465 
    3466         if (!(tdx_sysinfo->features.tdx_features0 & MD_FIELD_ID_FEATURES0_TOPOLOGY_ENUM))
    3467                 goto get_sysinfo_err;

here too?

    3468 
    3469         /*
    3470          * TDX has its own limit of maximum vCPUs it can support for all
    3471          * TDX guests in addition to KVM_MAX_VCPUS.  Userspace needs to
    3472          * query TDX guest's maximum vCPUs by checking KVM_CAP_MAX_VCPU
    3473          * extension on per-VM basis.
    3474          *
    3475          * TDX module reports such limit via the MAX_VCPU_PER_TD global
    3476          * metadata.  Different modules may report different values.
    3477          * Some old module may also not support this metadata (in which
    3478          * case this limit is U16_MAX).
    3479          *
    3480          * In practice, the reported value reflects the maximum logical
    3481          * CPUs that ALL the platforms that the module supports can
    3482          * possibly have.
    3483          *
    3484          * Simply forwarding the MAX_VCPU_PER_TD to userspace could
    3485          * result in an unpredictable ABI.  KVM instead always advertise
    3486          * the number of logical CPUs the platform has as the maximum
    3487          * vCPUs for TDX guests.
    3488          *
    3489          * Make sure MAX_VCPU_PER_TD reported by TDX module is not
    3490          * smaller than the number of logical CPUs, otherwise KVM will
    3491          * report an unsupported value to userspace.
    3492          *
    3493          * Note, a platform with TDX enabled in the BIOS cannot support
    3494          * physical CPU hotplug, and TDX requires the BIOS has marked
    3495          * all logical CPUs in MADT table as enabled.  Just use
    3496          * num_present_cpus() for the number of logical CPUs.
    3497          */
    3498         td_conf = &tdx_sysinfo->td_conf;
    3499         if (td_conf->max_vcpus_per_td < num_present_cpus()) {
    3500                 pr_err("Disable TDX: MAX_VCPU_PER_TD (%u) smaller than number of logical CPUs (%u).\n",
    3501                                 td_conf->max_vcpus_per_td, num_present_cpus());
    3502                 r = -EINVAL;
    3503                 goto get_sysinfo_err;
    3504         }
    3505 
    3506         if (misc_cg_set_capacity(MISC_CG_RES_TDX, tdx_get_nr_guest_keyids())) {
    3507                 r = -EINVAL;
    3508                 goto get_sysinfo_err;
    3509         }
    3510 
    3511         /*
    3512          * Leave hardware virtualization enabled after TDX is enabled
    3513          * successfully.  TDX CPU hotplug depends on this.
    3514          */
    3515         return 0;
    3516 
    3517 get_sysinfo_err:
    3518         __tdx_cleanup();
    3519 tdx_bringup_err:
    3520         kvm_disable_virtualization();
    3521         return r;
    3522 }

regards,
dan carpenter

Re: [bug report] KVM: TDX: Get system-wide info about TDX module on initialization

[Tony Lindgren]

Hi,

On Tue, Sep 09, 2025 at 11:28:37AM +0300, Dan Carpenter wrote:
> Commit 61bb28279623 ("KVM: TDX: Get system-wide info about TDX module
> on initialization") from Oct 30, 2024 (linux-next), leads to the
> following Smatch static checker warning:
> 
> 	arch/x86/kvm/vmx/tdx.c:3464 __tdx_bringup()
> 	warn: missing error code 'r'

Thanks fix sent:

https://lore.kernel.org/kvm/20250909101638.170135-1-tony.lindgren@linux.intel.com/

Regards,

Tony