Re: [PATCH v3 22/28] Docs/x86/sgx: Add description for cgroup support

Haitao Huang
2023-07-14T20:01:44Z

Hi

On Wed, 12 Jul 2023 19:10:59 -0500, Randy Dunlap <rdunlap@infradead.org>
wrote:

>> +
>> +
>> +Cgroup Support
>> +==============
>> +
>> +The "sgx_epc" resource within the Miscellaneous cgroup controller
>> regulates
>> +distribution of SGX EPC memory, which is a subset of system RAM that
>> +is used to provide SGX-enabled applications with protected memory,
>> +and is otherwise inaccessible, i.e. shows up as reserved in
>> +/proc/iomem and cannot be read/written outside of an SGX enclave.
>> +
>> +Although current systems implement EPC by stealing memory from RAM,
>> +for all intents and purposes the EPC is independent from normal system
>> +memory, e.g. must be reserved at boot from RAM and cannot be converted
>> +between EPC and normal memory while the system is running. The EPC is
>> +managed by the SGX subsystem and is not accounted by the memory
>> +controller. Note that this is true only for EPC memory itself, i.e.
>> +normal memory allocations related to SGX and EPC memory, e.g. the
>> +backing memory for evicted EPC pages, are accounted, limited and
>> +protected by the memory controller.
>> +
>> +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).
>> +The SGX EPC subsystem is analogous to the memory subsytem, and
>> +it implements limit and protection models for EPC memory.
>> +
>> +SGX EPC Interface Files
>> +-----------------------
>> +
>> +For a generic description of the Miscellaneous controller interface
>> +files, please see Documentation/admin-guide/cgroup-v2.rst
>> +
>> +All SGX EPC memory amounts are in bytes unless explicitly stated
>> +otherwise. If a value which is not PAGE_SIZE aligned is written,
>> +the actual value used by the controller will be rounded down to
>> +the closest PAGE_SIZE multiple.
>> +
>> + misc.capacity
>> + A read-only flat-keyed file shown only in the root cgroup.
>> + The sgx_epc resource will show the total amount of EPC
>> + memory available on the platform.
>> +
>> + misc.current
>> + A read-only flat-keyed file shown in the non-root cgroups.
>> + The sgx_epc resource will show the current active EPC memory
>> + usage of the cgroup and its descendants. EPC pages that are
>> + swapped out to backing RAM are not included in the current
>> count.
>> +
>> + misc.max
>> + A read-write single value file which exists on non-root
>> + cgroups. The sgx_epc resource will show the EPC usage
>> + hard limit. The default is "max".
>> +
>> + If a cgroup's EPC usage reaches this limit, EPC allocations,
>> + e.g. for page fault handling, will be blocked until EPC can
>> + be reclaimed from the cgroup. If EPC cannot be reclaimed in
>> + a timely manner, reclaim will be forced, e.g. by ignoring LRU.
>> +
>> + misc.events
>> + A read-write flat-keyed file which exists on non-root cgroups.
>> + Writes to the file reset the event counters to zero. A value
>> + change in this file generates a file modified event.
>> +
>> + max
>> + The number of times the cgroup has triggered a reclaim
>> + due to its EPC usage approaching (or exceeding) its max
>> + EPC boundary.
>
> The indentation here (above) is a little confusing.
> Is this formatted the way that is intended?
>
max here is an entry in the misc.events file. So it needs be indented a
subsection.
But I see spaces are used for indentation in sections above(misc.max,
misc.current and misc.capacity), and tabs are used in this section. So I
think maybe that's causing the confusing?
I'll fix them using all tabs.

Thanks
Haitao