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Subject: 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
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Hi, Reinette, thanks for your great contribution for EDMM Linux kernel patc=
h. 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=E2=80=99s pages. After driver invokes EN=
CLS[EMODPR] to restrict the page=E2=80=99s permission, it should then invok=
e 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 `__em=
odpr(=E2=80=A6)` 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 enclav=
e pages=E2=80=99 permission restriction, instead of N times (N =3D `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=