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Date:   Mon, 29 Aug 2022 13:34:20 -0700
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Subject: Re: [PATCH v11 1/3] x86/tdx: Add TDX Guest attestation interface
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To:     Dave Hansen <dave.hansen@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        Shuah Khan <shuah@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kai Huang <kai.huang@intel.com>,
        Wander Lairson Costa <wander@redhat.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
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        khalid.elmously@canonical.com, philip.cox@canonical.com,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
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From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
In-Reply-To: <12ab0a8a-a286-4f21-3b44-a506a6c2d008@intel.com>
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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