linux-kernel - Re: [PATCH V5 15/31] x86/sgx: Support restricting of enclave page permissions

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Date:   Thu, 1 Sep 2022 23:55:54 +0800
From:   zhubojun <bojun.zhu@...look.com>
To:     reinette.chatre@...el.com
Cc:     bp@...en8.de, cathy.zhang@...el.com, cedric.xing@...el.com,
        dave.hansen@...ux.intel.com, haitao.huang@...el.com, hpa@...or.com,
        jarkko@...nel.org, kai.huang@...el.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-sgx@...r.kernel.org, luto@...nel.org,
        mark.shanahan@...el.com, mingo@...hat.com, seanjc@...gle.com,
        shuah@...nel.org, tglx@...utronix.de, vijay.dhanraj@...el.com,
        x86@...nel.org
Subject: Re: [PATCH V5 15/31] x86/sgx: Support restricting of enclave page
 permissions

Hi, Reinette, thanks for your great contribution for EDMM Linux kernel patch. I am trying to follow the newest patch now, and I have some questions on it.

It seems that `sgx_enclave_restrict_permissions()` is able to do permission restrictions for multiple enclave’s pages. After driver invokes ENCLS[EMODPR] to restrict the page’s permission, it should then invoke ENCLS[ETRACK] and send IPIs to ensure stale TLB entries have been flushed. Only in this way, ENCLU[EACCEPT] inside enclave can only succeed.

Current implementation invokes `sgx_enclave_etrack(encl)` after every `__emodpr(…)` in the for loop. My question is:

Can we move the `sgx_enclave_etrack(encl)` out of the for loop? After doing so, `sgx_enclave_etrack(encl)` is invoked **one** time for multiple enclave pages’ permission restriction, instead of N times (N = `modp -> length / PAGE_SIZE`). We may gain some performance optimization from it.

Please correct my if my understanding is incorrect. Looking forward to your reply and Thanks for your time!

BR,
Bojun