linux-kernel - Re: [PATCH v2 1/6] x86/tdx: Add TDREPORT TDX Module call support

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Date:   Thu, 8 Jul 2021 16:20:28 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Peter H Anvin <hpa@...or.com>, Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/6] x86/tdx: Add TDREPORT TDX Module call support

Hi,

On 7/8/21 4:07 PM, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 7/8/21 1:16 AM, Xiaoyao Li wrote:
>>
>> Sorry I guess I didn't state it clearly during internal review.
>>
>> I suggest something like this
>>
>> if (ret != TDCALL_SUCCESS) {
>>      if (TDCALL_RETURN_CODE(ret) == TDCALL_INVALID_OPERAND)
>>          return -EINVAL;
>>      else if (TDCALL_RETURN_CODE(ret) == TDCALL_OPERAND_BUSY)
>>          return -EBUSY;
>>      else
>>          return -EFAULT; //I'm not sure if -EFAULT is proper.
>> }
> 
> As per current spec, TDCALL_INVALID_OPERAND, TDCALL_OPERAND_BUSY and
> 0 are the only possible return values. So I have checked for failure case
> in if condition and returned success by default. Any reason for specifically
> checking for success code ?

Yes, new error codes might be introduced and you might forget to
update this (or other) checks.

Checking for errors really MUST always be done by checking for
ret != success (typically ret != 0 or ret < 0).

Only checking for known error codes means that if somehow an
unknown error code gets thrown this gets treated as success,
which is not acceptable behavior.

Regards,

Hans