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

[Haitao Huang]

Hi

On Wed, 12 Jul 2023 19:10:59 -0500, Randy Dunlap <rdunlap@xxxxxxxxxxxxx>  
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