On Tue, Mar 08, 2022 at 11:16:19AM -0800, Reinette Chatre wrote:
> Hi,
>
> On 3/3/2022 2:38 PM, Jarkko Sakkinen wrote:
> > There is a limited amount of SGX memory (EPC) on each system. When that
> > memory is used up, SGX has its own swapping mechanism which is similar
> > in concept but totally separate from the core mm/* code. Instead of
> > swapping to disk, SGX swaps from EPC to normal RAM. That normal RAM
> > comes from a shared memory pseudo-file and can itself be swapped by the
> > core mm code. There is a hierarchy like this:
> >
> > EPC <-> shmem <-> disk
> >
> > After data is swapped back in from shmem to EPC, the shmem backing
> > storage needs to be freed. Currently, the backing shmem is not freed.
> > This effectively wastes the shmem while the enclave is running. The
> > memory is recovered when the enclave is destroyed and the backing
> > storage freed.
> >
> > Sort this out by freeing memory with shmem_truncate_range(), as soon as
> > a page is faulted back to the EPC. In addition, free the memory for
> > PCMD pages as soon as all PCMD's in a page have been marked as unused
> > by zeroing its contents.
> >
> > Reported-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
> > Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
>
> I can reliably reproduce the issue this patch aims to solve by creating
> a virtual machine that has a significant portion of its memory consumed
> by EPC:
>
> qemu-system-x86_64 -smp 4 -m 4G\
> -enable-kvm \
> -cpu host,+sgx-provisionkey \
> -object memory-backend-ram,size=2G,host-nodes=0,policy=bind,id=node0 \
> -object memory-backend-epc,id=mem0,size=1536M,prealloc=on,host-nodes=0,policy=bind \
> -numa node,nodeid=0,cpus=0-1,memdev=node0 \
> -object memory-backend-ram,size=2G,host-nodes=1,policy=bind,id=node1 \
> -object memory-backend-epc,id=mem1,size=1536M,prealloc=on,host-nodes=1,policy=bind \
> -numa node,nodeid=1,cpus=2-3,memdev=node1 \
> -M sgx-epc.0.memdev=mem0,sgx-epc.0.node=0,sgx-epc.1.memdev=mem1,sgx-epc.1.node=1 \
> ...
>
> Before this patch, running the very stressful SGX2 over subscription test case
> (unclobbered_vdso_oversubscribed_remove) in this environment always triggers
> the oom-killer but no amount of tasks killed can save the system
> with it always ending deadlocked on memory:
>
> [ 58.642719] Tasks state (memory values in pages):
> [ 58.644324] [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name
> [ 58.647237] [ 195] 0 195 3153 197 45056 0 -1000 systemd-udevd
> [ 58.650238] [ 281] 0 281 1836367 0 10817536 0 0 test_sgx
> [ 58.653088] Out of memory and no killable processes...
> [ 58.654832] Kernel panic - not syncing: System is deadlocked on memory
>
> After applying this patch I was able to run SGX2 selftest
> unclobbered_vdso_oversubscribed_remove ten times successfully.
>
> Tested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Thank you.
> Reinette
BR, Jarkko
