linux-kernel - Re: [PATCH RFC v3] x86/sgx: Add /proc/sys/kernel/sgx/total

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Message-ID: <0c935066-008d-b023-7dc3-f4e0ac1b3d20@intel.com>
Date:   Wed, 11 Aug 2021 07:30:13 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH RFC v3] x86/sgx: Add /proc/sys/kernel/sgx/total_mem

On 8/10/21 8:21 PM, Jarkko Sakkinen wrote:
> +The following sysctl files can be found in the ``/proc/sys/kernel/sgx/`` directory:
> +
> +``total_mem``
> +	The total amount of SGX protected memory in bytes available in the system
> +	available for use. In other words, it describes the size of the Enclave
> +	Page Cache (EPC).

I've been acting as if /proc is deprecated for new stuff.  Shouldn't
this be going in sysfs?

I figured, at some point, someone is going to ask for NUMA statistics.
That would tend to point in the direction of us needing something in:

	/sys/devices/system/node/nodeN/

Maybe 'sgxinfo' or 'sgxstat' to go along with 'meminfo'.

But, we'll probably also end up needing some stats for other things.
Folks have, for instance, asked for a counter of the number of
instantiated enclaves.

We could also use the drivers' namespaces:

	/sys/class/misc/sgx_enclave
	/sys/class/misc/sgx_provision
	/sys/class/misc/sgx_vepc

although that is a bit awkward for reporting global resources like memory.

We could create a platform device just for these stats, say:

	/sys/bus/platform/devices/sgx

But I think platform devices are rather highly scrutinized these days.
I'm not sure if SGX counts as one.

/sys/kernel also appears to be a bit of a free-for-all.  Perhaps it
could go in:

	/sys/kernel/sgx
or
	/sys/kernel/enclaves

The other crazy thing we could try would be to just hijack core mm
mechanisms:

	/proc/{meminfo,vmstat}
	/sys/devices/system/node/nodeN/{vmstat,meminfo}

Then we can just use the existing counter infrastructure, which I think
gets us into /sys and /proc.  I'm not sure the mm folks would be fond of
this for something arch and vendor specific, though.

In any case, ABIs are hard and SGX is weird.  News at 11.