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SubjectRe: [PATCH v8 06/16] x86/virt/tdx: Get information about TDX module and TDX-capable memory
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On 1/9/23 02:25, Huang, Kai wrote:
> On Fri, 2023-01-06 at 09:46 -0800, Dave Hansen wrote:
...
>>> Note not all members in the 1024 bytes TDX module information are used
>>> (even by the KVM).
>>
>> I'm not sure what this has to do with anything.
>
> You mentioned in v7 that:
>>>> This is also a great place to mention that the tdsysinfo_struct
contains
>>> a *lot* of gunk which will not be used for a bit or that may never get
>>> used.
>
> https://lore.kernel.org/linux-mm/cc195eb6499cf021b4ce2e937200571915bfe66f.camel@intel.com/T/#m168e619aac945fa418ccb1d6652113003243d895
>
> Perhaps I misunderstood something but I was trying to address this.
>
> Should I remove this sentence?

If someone goes looking at this patch, the see tdsysinfo_struct with
something like two dozen defined fields. But, very few of them get used
in this patch. Why? Just saying that they are unused is a bit silly.

The 'tdsysinfo_struct' is fairly large (1k) and contains a lot
of info about the TD. Fully define the entire structure, but
only use the fields necessary to build the PAMT and TDMRs and
pr_info() some basics about the module.

The rest of the fields will get used... (by kvm? never??)

...
>>> + struct tdsysinfo_struct *sysinfo = &PADDED_STRUCT(tdsysinfo);
>>> + int ret;
>>> +
>>> + ret = tdx_get_sysinfo(sysinfo, cmr_array);
>>> + if (ret)
>>> + goto out;
>>> +
>>> /*
>>> * TODO:
>>> *
>>> - * - Get TDX module information and TDX-capable memory regions.
>>> * - Build the list of TDX-usable memory regions.
>>> * - Construct a list of TDMRs to cover all TDX-usable memory
>>> * regions.
>>> @@ -166,7 +239,9 @@ static int init_tdx_module(void)
>>> *
>>> * Return error before all steps are done.
>>> */
>>> - return -EINVAL;
>>> + ret = -EINVAL;
>>> +out:
>>> + return ret;
>>> }
>>
>> I'm going to be lazy and not look into the future. But, you don't need
>> the "out:" label here, yet. It doesn'serve any purpose like this, so
>> why introduce it here?
>
> The 'out' label is here because of below code:
>
> ret = tdx_get_sysinfo(...);
> if (ret)
> goto out;
>
> If I don't have 'out' label here in this patch, do you mean something below?
>
> ret = tdx_get_sysinfo(...);
> if (ret)
> return ret;
>
> /*
> * TODO:
> * ...
> * Return error before all steps are done.
> */
> return -EINVAL;

Yes, if you remove the 'out:' label like you've shown in your reply,
it's actually _less_ code. The labels are really only necessary when
you have common work to "undo" something before returning from the
function. Here, you can just return.

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