linux-kernel - Re: [PATCH 13/25] x86/sgx: Support adding of pages to initialized enclave

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Date:   Mon, 13 Dec 2021 14:12:57 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
CC:     <dave.hansen@...ux.intel.com>, <tglx@...utronix.de>,
        <bp@...en8.de>, <luto@...nel.org>, <mingo@...hat.com>,
        <linux-sgx@...r.kernel.org>, <x86@...nel.org>, <seanjc@...gle.com>,
        <kai.huang@...el.com>, <cathy.zhang@...el.com>,
        <cedric.xing@...el.com>, <haitao.huang@...el.com>,
        <mark.shanahan@...el.com>, <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/25] x86/sgx: Support adding of pages to initialized
 enclave

Hi Jarkko,

On 12/11/2021 12:00 AM, Jarkko Sakkinen wrote:
> On Mon, 2021-12-06 at 13:44 -0800, Reinette Chatre wrote:
>> On 12/4/2021 3:13 PM, Jarkko Sakkinen wrote:
>>> On Wed, Dec 01, 2021 at 11:23:11AM -0800, Reinette Chatre wrote:

...

>>>> Accessing an uninitialized address from outside the enclave also triggers
>>>> this flow but the page will remain in PENDING state until accepted from
>>>> within the enclave.
>>>
>>> What does it mean being in PENDING state, and more imporantly, what is
>>> PENDING state? What does a memory access within enclave cause when it
>>> touch a page within this state?
>>
>> The PENDING state is the enclave page state from the SGX hardware's
>> perspective. The OS uses the ENCLS[EAUG] SGX2 function to add a new page
>> to the enclave but from the SGX hardware's perspective it would be in a
>> PENDING state until the enclave accepts the page. An access to the page
>> in PENDING state would result in a page fault.
>>
>>
>>> I see a lot of text in the commit message but zero mentions about EPCM
>>> expect this one sudden mention about PENDING field without attaching
>>> it to anything concrete.
>>
>> My apologies - I will add this to this changelog. This matches your
>> request to describe the __eaug() wrapper introduced in patch 02/25.
>> Would you like me to duplicate this information here and in that patch
>> (a new patch dedicated to the __eaug() wrapper) or would you be ok if I
>> introduce the wrappers all together briefly as in the example you
>> provide and then detail the flows where the wrappers are used - like
>> this patch?
> 
> I think it would be a good place to describe these details in 02/25,
> and skip them in rest of the patches.
> 

Will do. I do think describing this amount of detail for the new SGX2 
functions would be too much for a single patch so I currently plan to 
split that (02/25) patch into a new patch per SGX2 instruction. Is that 
ok with you or would you like to keep it in a single patch?

Reinette