linux-kernel - Re: [tip: x86/urgent] x86/tdx: Prepare for using "INFO" call for a second purpose

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Date:   Mon, 7 Nov 2022 05:26:27 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        x86@...nel.org
Subject: Re: [tip: x86/urgent] x86/tdx: Prepare for using "INFO" call for a
 second purpose

On 11/6/22 11:50, Borislav Petkov wrote:
> On Sun, Nov 06, 2022 at 09:02:27AM -0800, Dave Hansen wrote:
>> It's fine for now, except that the naming on this:
>>
>> -	tdx_parse_tdinfo(&cc_mask);
>> +	cc_mask = tdx_parse_tdinfo();
>>
>> is a bit funky since tdx_parse_tdinfo() is doing a couple of things
> Yeah, that was the next thing that was bothering me.
> 
>> and will need to return a second item shortly.
> Well, then rename this one back to get_cc_mask() and have a new function
> return the second item?

That's doable.  It would look something like what I've attached for now.
 The only downside to this is making two tdx_module_call(TDX_GET_INFO...)
calls.  That seems a bit wasteful, but it's not the end of the world.
It would look something like the attached patch.

I kinda like the idea of making one tdx_module_call() and parsing it all
in one place.  The calls are kinda slow, but two of them versus one
isn't going to hurt anybody.

The other thing I considered was keeping a temporary 'struct
tdx_guest_info' structure or something, filling it one, and parsing it
in get_cc_mask() and attribute checking functions.  But, that seemed
like overkill.
View attachment "tdinfo.patch" of type "text/x-patch" (1739 bytes)