linux-kernel - Re: [PATCH v11 1/3] x86/tdx: Add TDX Guest attestation interface driver

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Message-ID: <9e41582a-425d-5b85-a83a-9590388a0d40@linux.intel.com>
Date:   Mon, 29 Aug 2022 13:34:20 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v11 1/3] x86/tdx: Add TDX Guest attestation interface
 driver



On 8/29/22 1:28 PM, Dave Hansen wrote:
> On 8/29/22 13:09, Sathyanarayanan Kuppuswamy wrote:
>> With the changed format, we avoided the holes, but it still adds 7 bytes of padding.
>>
>> Total size of struct is 32 bytes.
>>
>> struct tdx_report_req {
>> 	__u64                      reportdata;           /*     0     8 */
>> 	__u64                      tdreport;             /*     8     8 */
>> 	__u32                      rpd_len;              /*    16     4 */
>> 	__u32                      tdr_len;              /*    20     4 */
>> 	__u8                       subtype;              /*    24     1 */
>>
>> 	/* size: 32, cachelines: 1, members: 5 */
>> 	/* padding: 7 */
>> 	/* last cacheline: 32 bytes */
>> };
> 
> Might as well make some use of the padding and add:
> 
> 	u8 reserved[7];
> 
> That will ensure that the entire structure is explicitly sized *AND*
> leave you room to add flags or other fun in the future without a new ABI.

Ok. I will add it in next version.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer