On Thu Sep 26, 2024 at 3:38 AM EEST, Kai Huang wrote: > > > On 26/09/2024 12:33 pm, Jarkko Sakkinen wrote: > > On Thu Sep 26, 2024 at 3:07 AM EEST, Kai Huang wrote: > >> > >> > >> On 23/09/2024 7:48 pm, Jarkko Sakkinen wrote: > >>> On Sun Sep 22, 2024 at 7:57 PM EEST, Jarkko Sakkinen wrote: > >>>>> On Sun Sep 22, 2024 at 7:27 PM EEST, Jarkko Sakkinen wrote: > >>>>>> Hi > >>>>>> > >>>>>> I started to look into this old issue with mm subsystem and SGX, i.e. > >>>>>> can we make SGX VMA's to merge together? > >>>>>> > >>>>>> This demonstrates the problem pretty well: > >>>>>> > >>>>>> https://lore.kernel.org/linux-sgx/884c7ea454cf2eb0ba2e95f7c25bd42018824f97.camel@xxxxxxxxxx/ > >>>>>> > >>>>>> It was result of brk() syscall being applied a few times. > >>>> > >>>> Briging some context here. This can be fixed in the run-time by book > >>>> keeping the ranges and doing unmapping/mapping. I guess this goes > >>>> beyond what mm should support? > >>>> > >>>> I thought to plain check this as it has been two years since my last > >>>> query on topic (if we could improve either the driver or mm somehow). > >>> > >>> In the past I've substituted kernel's mm merge code with user space > >>> replacement: > >>> > >>> https://github.com/enarx/mmledger/blob/main/src/lib.rs > >>> > >>> It's essentially a reimplementation of al stuff that goes into > >>> mm/mmap.c's vma_merge(). I cannot recall anymore whether merges > >>> which map over existing ranges were working correctly, i.e. was > >>> the issue only concerning adjacent VMA's. > >>> > >>> What I'm looking here is that can we make some cosntraints that > >>> if satisfied by the pfnmap code, it could leverage the code from > >>> vma_merge(). Perhaps by making explicit call to vma_merge()? > >>> I get that implicit use moves too much responsibility to the mm > >>> subsystem. > >>> > >> > >> Hi Jarkko, > >> > >> Just want to understand more on the background: > >> > >> Are you seeing any real problem due to needing a lot of mmap()s to the > >> same enclave, or it is just a problem that doesn't look nice and you > >> want to resolve? > >> > >> I mean, this problem doesn't seem to be SGX-specific but a common one > >> for VMAs with VM_PFNMAP (any bit in VM_SPECIAL), e.g., from random > >> device drivers with mmap() support. We will need a good justification > >> if we want to make any core-mm change, if any, for this. > > > > It requires essentially replicating core mm in user space. > > > > Is there any real problem if we don't do this at all (neither in core mm > nor in userspace)? 7f8f00000000-7f8f00009000 r--s 00000000 00:05 84 /dev/sgx_enclave 7f8f00009000-7f8f00034000 rw-s 00000000 00:05 84 /dev/sgx_enclave 7f8f00034000-7f8f000ff000 r-xs 00000000 00:05 84 /dev/sgx_enclave 7f8f000ff000-7f8f00201000 ---p 00000000 00:00 0 7f8f00201000-7f8f003fc000 rw-s 00000000 00:05 84 /dev/sgx_enclave 7f8f003fc000-7f8f003fd000 rw-s 00000000 00:05 84 /dev/sgx_enclave 7f8f003fd000-7f8f00400000 rw-s 00000000 00:05 84 /dev/sgx_enclave 7f8f00400000-7f8f00643000 r--s 00000000 00:05 84 /dev/sgx_enclave 7f8f00643000-7f8f0197b000 r-xs 00000000 00:05 84 /dev/sgx_enclave 7f8f0197b000-7f8f01bab000 r--s 00000000 00:05 84 /dev/sgx_enclave 7f8f01bab000-7f8f01fa7000 rw-s 00000000 00:05 84 /dev/sgx_enclave 7f8f01fa7000-7f8f08000000 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