linux-kernel - Re: [PATCH v17 2/3] virt: Add TDX guest driver

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Date:   Wed, 9 Nov 2022 07:36:21 -0800
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Wander Lairson Costa <wander@...hat.com>
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>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.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 v17 2/3] virt: Add TDX guest driver



On 11/9/22 6:24 AM, Wander Lairson Costa wrote:
>> +	reportdata = kmalloc(TDX_REPORTDATA_LEN, GFP_KERNEL);
>> +	if (!reportdata)
>> +		return -ENOMEM;
>> +
>> +	tdreport = kzalloc(TDX_REPORT_LEN, GFP_KERNEL);
>> +	if (!tdreport) {
>> +		ret = -ENOMEM;
>> +		goto out;
>> +	}
> Isn't simpler just allocating a struct tdx_report_req? You would save
> one allocation and a few lines of code.
> 

TDG.MR.TDCALL expects reportdata and tdreport buffers to be size aligned. So,
allocating them together with sizeof(struct tdx report req) will not work. We
can get around this by allocating a slightly larger buffer size. However, because
it is not a time-critical path, I believe that allocating two separate buffers
for input/output is simpler.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer