Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

Huang, Kai
2024-04-03T22:26:35Z

On 4/04/2024 6:24 am, Yamahata, Isaku wrote:
> On Thu, Mar 28, 2024 at 12:33:35PM +1300,
> "Huang, Kai" <kai.huang@intel.com> wrote:
>
>>> + kvm_tdx->tdr_pa = tdr_pa;
>>> +
>>> + for_each_online_cpu(i) {
>>> + int pkg = topology_physical_package_id(i);
>>> +
>>> + if (cpumask_test_and_set_cpu(pkg, packages))
>>> + continue;
>>> +
>>> + /*
>>> + * Program the memory controller in the package with an
>>> + * encryption key associated to a TDX private host key id
>>> + * assigned to this TDR. Concurrent operations on same memory
>>> + * controller results in TDX_OPERAND_BUSY. Avoid this race by
>>> + * mutex.
>>> + */
>>
>> IIUC the race can only happen when you are creating multiple TDX guests
>> simulatenously? Please clarify this in the comment.
>>
>> And I even don't think you need all these TDX module details:
>>
>> /*
>> * Concurrent run of TDH.MNG.KEY.CONFIG on the same
>> * package resluts in TDX_OPERAND_BUSY. When creating
>> * multiple TDX guests simultaneously this can run
>> * concurrently. Take the per-package lock to
>> * serialize.
>> */
>
> As pointed by Chao, those mutex will be dropped.
> https://lore.kernel.org/kvm/ZfpwIespKy8qxWWE@chao-email/
> Also we would simplify cpu masks to track which package is online/offline,
> which cpu to use for each package somehow.

Please see my reply there. I might be missing something, though.

>
>
>>> + mutex_lock(&tdx_mng_key_config_lock[pkg]);
>>> + ret = smp_call_on_cpu(i, tdx_do_tdh_mng_key_config,
>>> + &kvm_tdx->tdr_pa, true);
>>> + mutex_unlock(&tdx_mng_key_config_lock[pkg]);
>>> + if (ret)
>>> + break;
>>> + }
>>> + cpus_read_unlock();
>>> + free_cpumask_var(packages);
>>> + if (ret) {
>>> + i = 0;
>>> + goto teardown;
>>> + }
>>> +
>>> + kvm_tdx->tdcs_pa = tdcs_pa;
>>> + for (i = 0; i < tdx_info->nr_tdcs_pages; i++) {
>>> + err = tdh_mng_addcx(kvm_tdx->tdr_pa, tdcs_pa[i]);
>>> + if (err == TDX_RND_NO_ENTROPY) {
>>> + /* Here it's hard to allow userspace to retry. */
>>> + ret = -EBUSY;
>>> + goto teardown;
>>> + }
>>> + if (WARN_ON_ONCE(err)) {
>>> + pr_tdx_error(TDH_MNG_ADDCX, err, NULL);
>>> + ret = -EIO;
>>> + goto teardown;
>>> + }
>>> + }
>>> +
>>> + /*
>>> + * Note, TDH_MNG_INIT cannot be invoked here. TDH_MNG_INIT requires a dedicated
>>> + * ioctl() to define the configure CPUID values for the TD.
>>> + */
>>
>> Then, how about renaming this function to __tdx_td_create()?
>
> So do we want to rename also ioctl name for consistency?
> i.e. KVM_TDX_INIT_VM => KVM_TDX_CREATE_VM.

Hmm.. but this __tdx_td_create() (the __tdx_td_init() in this patch) is
called via kvm_x86_ops->vm_init(), but not IOCTL()?

If I read correctly, only TDH.MNG.INIT is called via IOCTL(), in that
sense it makes more sense to name the IOCTL() as KVM_TDX_INIT_VM.

>
> I don't have strong opinion those names. Maybe
> KVM_TDX_{INIT, CREATE, or CONFIG}_VM?
> And we can rename the function name to match it.
>