Re: [PATCH v6 00/12] Add Cgroup support for SGX EPC memory

Jarkko Sakkinen
2023-11-06T03:26:53Z

On Mon, 2023-10-30 at 11:20 -0700, Haitao Huang wrote:
> SGX Enclave Page Cache (EPC) memory allocations are separate from normal RAM allocations, and
> are managed solely by the SGX subsystem. The existing cgroup memory controller cannot be used
> to limit or account for SGX EPC memory, which is a desirable feature in some environments,
> e.g., support for pod level control in a Kubernates cluster on a VM or baremetal host [1,2].
>
> This patchset implements the support for sgx_epc memory within the misc cgroup controller. The
> user can use the misc cgroup controller to set and enforce a max limit on total EPC usage per
> cgroup. The implementation reports current usage and events of reaching the limit per cgroup as
> well as the total system capacity.
>
> With the EPC misc controller enabled, every EPC page allocation is accounted for a cgroup's
> usage, reflected in the 'sgx_epc' entry in the 'misc.current' interface file of the cgroup.
> Much like normal system memory, EPC memory can be overcommitted via virtual memory techniques
> and pages can be swapped out of the EPC to their backing store (normal system memory allocated
> via shmem, accounted by the memory controller). When the EPC usage of a cgroup reaches its hard
> limit ('sgx_epc' entry in the 'misc.max' file), the cgroup starts a reclamation process to swap
> out some EPC pages within the same cgroup and its descendant to their backing store. Although
> the SGX architecture supports swapping for all pages, to avoid extra complexities, this
> implementation does not support swapping for certain page types, e.g.  Version Array(VA) pages,
> and treat them as unreclaimable pages.  When the limit is reached but nothing left in the
> cgroup for reclamation, i.e., only unreclaimable pages left, any new EPC allocation in the
> cgroup will result in an ENOMEM error.
>
> The EPC pages allocated for guest VMs by the virtual EPC driver are not reclaimable by the host
> kernel [5]. Therefore they are also treated as unreclaimable from cgroup's point of view.  And
> the virtual EPC driver translates an ENOMEM error resulted from an EPC allocation request into
> a SIGBUS to the user process.
>
> This work was originally authored by Sean Christopherson a few years ago, and previously
> modified by Kristen C. Accardi to utilize the misc cgroup controller rather than a custom
> controller. I have been updating the patches based on review comments since V2 [3, 4, 10],
> simplified the implementation/design and fixed some stability issues found from testing.
>
> The patches are organized as following:
> - Patches 1-3 are prerequisite misc cgroup changes for adding new APIs, structs, resource
>   types.
> - Patch 4 implements basic misc controller for EPC without reclamation.
> - Patches 5-9 prepare for per-cgroup reclamation.
>     * Separate out the existing infrastructure of tracking reclaimable pages
>       from the global reclaimer(ksgxd) to a newly created LRU list struct.
>     * Separate out reusable top-level functions for reclamation.
> - Patch 10 adds support for per-cgroup reclamation.
> - Patch 11 adds documentation for the EPC cgroup.
> - Patch 12 adds test scripts.
>
> I appreciate your review and providing tags if appropriate.
>
> ---
> V6:
> - Dropped OOM killing path, only implement non-preemptive enforcement of max limit (Dave, Michal)
> - Simplified reclamation flow by taking out sgx_epc_reclaim_control, forced reclamation by
>   ignoring 'age".
> - Restructured patches: split misc API + resource types patch and the big EPC cgroup patch
>   (Kai, Michal)
> - Dropped some Tested-by/Reviewed-by tags due to significant changes
> - Added more selftests
>
> v5:
> - Replace the manual test script with a selftest script.
> - Restore the "From" tag for some patches to Sean (Kai)
> - Style fixes (Jarkko)
>
> v4:
> - Collected "Tested-by" from Mikko. I kept it for now as no functional changes in v4.
> - Rebased on to v6.6_rc1 and reordered patches as described above.
> - Separated out the bug fixes [7,8,9]. This series depend on those patches. (Dave, Jarkko)
> - Added comments in commit message to give more preview what's to come next. (Jarkko)
> - Fixed some documentation error, gap, style (Mikko, Randy)
> - Fixed some comments, typo, style in code (Mikko, Kai)
> - Patch format and background for reclaimable vs unreclaimable (Kai, Jarkko)
> - Fixed typo (Pavel)
> - Exclude the previous fixes/enhancements for self-tests. Patch 18 now depends on series [6]
> - Use the same to list for cover and all patches. (Solo)
>
> v3:
>
> - Added EPC states to replace flags in sgx_epc_page struct. (Jarkko)
> - Unrolled wrappers for cond_resched, list (Dave)
> - Separate patches for adding reclaimable and unreclaimable lists. (Dave)
> - Other improvements on patch flow, commit messages, styles. (Dave, Jarkko)
> - Simplified the cgroup tree walking with plain
>   css_for_each_descendant_pre.
> - Fixed race conditions and crashes.
> - OOM killer to wait for the victim enclave pages being reclaimed.
> - Unblock the user by handling misc_max_write callback asynchronously.
> - Rebased onto 6.4 and no longer base this series on the MCA patchset.
> - Fix an overflow in misc_try_charge.
> - Fix a NULL pointer in SGX PF handler.
> - Updated and included the SGX selftest patches previously reviewed. Those
>   patches fix issues triggered in high EPC pressure required for cgroup
>   testing.
> - Added test scripts to help setup and test SGX EPC cgroups.
>
> [1]https://lore.kernel.org/all/DM6PR21MB11772A6ED915825854B419D6C4989@DM6PR21MB1177.namprd21.prod.outlook.com/
> [2]https://lore.kernel.org/all/ZD7Iutppjj+muH4p@himmelriiki/
> [3]https://lore.kernel.org/all/20221202183655.3767674-1-kristen@linux.intel.com/
> [4]https://lore.kernel.org/linux-sgx/20230712230202.47929-1-haitao.huang@linux.intel.com/
> [5]Documentation/arch/x86/sgx.rst, Section "Virtual EPC"
> [6]https://lore.kernel.org/linux-sgx/20220905020411.17290-1-jarkko@kernel.org/
> [7]https://lore.kernel.org/linux-sgx/ZLcXmvDKheCRYOjG@slm.duckdns.org/
> [8]https://lore.kernel.org/linux-sgx/20230721120231.13916-1-haitao.huang@linux.intel.com/
> [9]https://lore.kernel.org/linux-sgx/20230728051024.33063-1-haitao.huang@linux.intel.com/
> [10]https://lore.kernel.org/all/20230923030657.16148-1-haitao.huang@linux.intel.com/
>
> Haitao Huang (2):
>   x86/sgx: Introduce EPC page states
>   selftests/sgx: Add scripts for EPC cgroup testing
>
> Kristen Carlson Accardi (5):
>   cgroup/misc: Add per resource callbacks for CSS events
>   cgroup/misc: Export APIs for SGX driver
>   cgroup/misc: Add SGX EPC resource type
>   x86/sgx: Implement basic EPC misc cgroup functionality
>   x86/sgx: Implement EPC reclamation for cgroup
>
> Sean Christopherson (5):
>   x86/sgx: Add sgx_epc_lru_list to encapsulate LRU list
>   x86/sgx: Use sgx_epc_lru_list for existing active page list
>   x86/sgx: Use a list to track to-be-reclaimed pages
>   x86/sgx: Restructure top-level EPC reclaim function
>   Docs/x86/sgx: Add description for cgroup support
>
>  Documentation/arch/x86/sgx.rst                |  74 ++++
>  arch/x86/Kconfig                              |  13 +
>  arch/x86/kernel/cpu/sgx/Makefile              |   1 +
>  arch/x86/kernel/cpu/sgx/encl.c                |   2 +-
>  arch/x86/kernel/cpu/sgx/epc_cgroup.c          | 319 ++++++++++++++++++
>  arch/x86/kernel/cpu/sgx/epc_cgroup.h          |  49 +++
>  arch/x86/kernel/cpu/sgx/main.c                | 245 +++++++++-----
>  arch/x86/kernel/cpu/sgx/sgx.h                 |  88 ++++-
>  include/linux/misc_cgroup.h                   |  42 +++
>  kernel/cgroup/misc.c                          |  52 ++-
>  .../selftests/sgx/run_epc_cg_selftests.sh     | 196 +++++++++++
>  .../selftests/sgx/watch_misc_for_tests.sh     |  13 +
>  12 files changed, 996 insertions(+), 98 deletions(-)
>  create mode 100644 arch/x86/kernel/cpu/sgx/epc_cgroup.c
>  create mode 100644 arch/x86/kernel/cpu/sgx/epc_cgroup.h
>  create mode 100755 tools/testing/selftests/sgx/run_epc_cg_selftests.sh
>  create mode 100755 tools/testing/selftests/sgx/watch_misc_for_tests.sh
>

Is this expected to work on NUC7?

Planning to test this next week (no time this week).

BR, Jarkko