linux-kernel - Re: [PATCH 07/25] x86/sgx: Move PTE zap code to separate function

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Date:   Thu, 6 Jan 2022 09:46:35 -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 07/25] x86/sgx: Move PTE zap code to separate function

Hi Jarkko,

On 12/28/2021 6:55 AM, Jarkko Sakkinen wrote:
> On Mon, Dec 13, 2021 at 02:11:26PM -0800, Reinette Chatre wrote:
>> Hi Jarkko,
>>
>> On 12/10/2021 11:52 PM, Jarkko Sakkinen wrote:
>>> On Mon, 2021-12-06 at 13:30 -0800, Reinette Chatre wrote:
>>>> Hi Jarkko,
>>>>
>>>> On 12/4/2021 2:59 PM, Jarkko Sakkinen wrote:
>>>>> On Wed, Dec 01, 2021 at 11:23:05AM -0800, Reinette Chatre wrote:
>>>>>> The SGX reclaimer removes page table entries pointing to pages that are
>>>>>> moved to swap. SGX2 enables changes to pages belonging to an initialized
>>>>>> enclave, for example changing page permissions. Supporting SGX2 requires
>>>>>> this ability to remove page table entries that is available in the
>>>>>> SGX reclaimer code.
>>>>>
>>>>> Missing: why SGX2 requirest this?
>>>>
>>>> The above paragraph states that SGX2 needs to remove page table entries
>>>> because it modifies page permissions. Could you please elaborate what is
>>>> missing?
>>>
>>> It does not say why SGX2 requires an ability to remove page table entries.
>>
>> Are you saying that modification of EPCM page permissions is not a reason to
>> remove page table entries pointing to those pages?
> 
> So you have:
> 
> "Supporting SGX2 requires this ability to remove page table entries that is
> available in the SGX reclaimer code"
> 
> Just write down where you need this ability (briefly).

Will do. I will expand the current permission changing text and also add the need
for this ability when regular pages are changed to TCS pages. TCS pages may not
be accessed by enclave code so when a regular page becomes a TCS page any page
table entries pointing to it should be removed.

Reinette