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Subject: Re: [RFC PATCH v2 0/3] An alternative __vdso_sgx_enter_enclave() to
 allow enclave/host parameter passing using untrusted stack
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org,
        akpm@linux-foundation.org, dave.hansen@intel.com,
        sean.j.christopherson@intel.com, serge.ayoun@intel.com,
        shay.katz-zamir@intel.com, haitao.huang@intel.com,
        kai.svahn@intel.com, kai.huang@intel.com
References: <cover.1555965327.git.cedric.xing@intel.com>
 <20190424062623.4345-1-cedric.xing@intel.com>
 <20190710111719.nnoedfo4wvbfghq7@linux.intel.com>
 <686e47d2-f45c-6828-39d1-48374925de6c@intel.com>
 <20190710224628.epjxwlpqqxdurmzo@linux.intel.com>
 <20190710231538.dkc7tyeyvns53737@linux.intel.com>
 <27cf0fc7-71c6-7dc1-f031-86bf887f1fe1@intel.com>
 <20190711093809.4ogxe25laeoyp4ve@linux.intel.com>
From:   "Xing, Cedric" <cedric.xing@intel.com>
Message-ID: <7774fb16-7e41-f504-f3c8-d2588859be48@intel.com>
Date:   Thu, 11 Jul 2019 12:51:13 -0700
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On 7/11/2019 2:38 AM, Jarkko Sakkinen wrote:
> On Wed, Jul 10, 2019 at 04:37:41PM -0700, Xing, Cedric wrote:
>> On 7/10/2019 4:15 PM, Jarkko Sakkinen wrote:
>>> On Thu, Jul 11, 2019 at 01:46:28AM +0300, Jarkko Sakkinen wrote:
>>>> On Wed, Jul 10, 2019 at 11:08:37AM -0700, Xing, Cedric wrote:
>>>>>> With these conclusions I think the current vDSO API is sufficient for
>>>>>> Linux.
>>>>>
>>>>> The new vDSO API is to support data exchange on stack. It has nothing to do
>>>>> with debugging. BTW, the community has closed on this.
>>>>
>>>> And how that is useful?
>>>>
>>>>> The CFI directives are for stack unwinding. They don't affect what the code
>>>>> does so you can just treat them as NOPs if you don't understand what they
>>>>> do. However, they are useful to not only debuggers but also exception
>>>>> handling code. libunwind also has a setjmp()/longjmp() implementation based
>>>>> on CFI directives.
>>>>
>>>> Of course I won't merge code of which usefulness I don't understand.
>>>
>>> I re-read the cover letter [1] because it usually is the place
>>> to "pitch" a feature.
>>>
>>> It fails to address two things:
>>>
>>> 1. How and in what circumstances is an untrusted stack is a better
>>>      vessel for handling exceptions than the register based approach
>>>      that we already have?
>>
>> We are not judging which vessel is better (or the best) among all possible
>> vessels. We are trying to enable more vessels. Every vessel has its pros and
>> cons so there's *no* single best vessel.
> 
> I think reasonable metric is actually the coverage of the Intel SDK
> based enclaves. How widely are they in the wild? If the user base is
> large, it should be reasonable to support this just based on that.

I don't know how many existing enclaves out there, but definitely larger 
than 0 (zero), while user base for the old API is definitely 0. What are 
you worrying, really?

> /Jarkko
>