On Thu, May 19, 2022 at 2:05 PM Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx> wrote: > > When the system runs out of enclave memory, SGX can reclaim EPC pages > by swapping to normal RAM. These backing pages are allocated via a > per-enclave shared memory area. Since SGX allows unlimited over > commit on EPC memory, the reclaimer thread can allocate a large > number of backing RAM pages in response to EPC memory pressure. > > When the shared memory backing RAM allocation occurs during > the reclaimer thread context, the shared memory is charged to > the root memory control group, and the shmem usage of the enclave > is not properly accounted for, making cgroups ineffective at > limiting the amount of RAM an enclave can consume. > > For example, when using a cgroup to launch a set of test > enclaves, the kernel does not properly account for 50% - 75% of > shmem page allocations on average. In the worst case, when > nearly all allocations occur during the reclaimer thread, the > kernel accounts less than a percent of the amount of shmem used > by the enclave's cgroup to the correct cgroup. > > SGX stores a list of mm_structs that are associated with > an enclave. Pick one of them during reclaim and charge that > mm's memcg with the shmem allocation. The one that gets picked > is arbitrary, but this list almost always only has one mm. The > cases where there is more than one mm with different memcg's > are not worth considering. > > Create a new function - sgx_encl_alloc_backing(). This function > is used whenever a new backing storage page needs to be > allocated. Previously the same function was used for page > allocation as well as retrieving a previously allocated page. > Prior to backing page allocation, if there is a mm_struct associated > with the enclave that is requesting the allocation, it is set > as the active memory control group. > > Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx> For the memcg part: Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
