linux-kernel - Re: [PATCH v3 09/21] x86/virt/tdx: Get information about TDX module and convertible memory

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Message-ID: <4aea41ea-211f-fbde-34e9-4c4467ebc848@intel.com>
Date:   Fri, 29 Apr 2022 10:47:52 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, len.brown@...el.com,
        tony.luck@...el.com, rafael.j.wysocki@...el.com,
        reinette.chatre@...el.com, dan.j.williams@...el.com,
        peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com
Subject: Re: [PATCH v3 09/21] x86/virt/tdx: Get information about TDX module
 and convertible memory

On 4/28/22 16:14, Kai Huang wrote:
> On Thu, 2022-04-28 at 07:06 -0700, Dave Hansen wrote:
>> On 4/27/22 17:15, Kai Huang wrote:
>>>> Couldn't we get rid of that comment if you did something like:
>>>>
>>>> 	ret = tdx_get_sysinfo(&tdx_cmr_array, &tdx_sysinfo);
>>>
>>> Yes will do.
>>>
>>>> and preferably make the variables function-local.
>>>
>>> 'tdx_sysinfo' will be used by KVM too.
>>
>> In other words, it's not a part of this series so I can't review whether
>> this statement is correct or whether there's a better way to hand this
>> information over to KVM.
>>
>> This (minor) nugget influencing the design also isn't even commented or
>> addressed in the changelog.
> 
> TDSYSINFO_STRUCT is 1024B and CMR array is 512B, so I don't think it should be
> in the stack.  I can change to use dynamic allocation at the beginning and free
> it at the end of the function.  KVM support patches can change it to static
> variable in the file.

2k of stack is big, but it isn't a deal breaker for something that's not
nested anywhere and that's only called once in a pretty controlled
setting and not in interrupt context.  I wouldn't cry about it.