rchatre / linux Goto Github PK

Hi, @rchatre , thanks for your great contribution for EDMM Linux kernel patch. I'm the person who is interested in the newer EDMM, and I'm trying to follow and understand the implementation from the newest EDMM kernel patch.

I have some questions on the current implementation sgx_enclave_modify_type(): Why remove the PTE in enclave's page table when we modify the page type from SGX_PAGE_TYPE_REG to SGX_PAGE_TYPE_TCS (Line 968 in arch/x86/kernel/cpu/sgx/ioctl.c) ? As mentioned in the Intel SDK SDM, the EMODT performed by kernel needs validation by EACCEPT inside enclave. If we remove the PTE mapping of TCS page here, subsequent EACCEPT will generate #PF exception, and the sgx_vma_fault() in arch/x86/kernel/cpu/sgx/encl.c will re-add the mapping (I have verified such flow on my machine by using the SGX SDK with newest EDMM support: https://github.com/intel/linux-sgx/tree/edmm_v5).

My question is: can we eliminate the operations in Line 953- Line 972 ? Such operations seem to remove the mappings which will be re-added by vma fault handler (sgx_vma_fault()). I'm new to Linux kernel development, please correct me if my understanding is incorrect.

Looking forward to your reply!