linux-kernel - Re: [PATCH v9 2/2] x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node

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Message-ID: <3ffafe28-e770-a285-98d0-1379271ba36d@intel.com>
Date:   Fri, 29 Oct 2021 10:00:35 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     reinette.chatre@...el.com, tony.luck@...el.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org
Subject: Re: [PATCH v9 2/2] x86/sgx: Add an attribute for the amount of SGX
 memory in a NUMA node

On 10/29/21 5:18 AM, Jarkko Sakkinen wrote:
> +What:		/sys/devices/system/node/nodeX/sgx/size
> +Date:		October 2021
> +Contact:	Jarkko Sakkinen <jarkko@...nel.org>

I don't think we should do something *entirely* SGX-specific here.  The
only question to me is whether any non-SGX users want something like
this and who they are.

Here are some ideas I like more than an "sgx/" directory:

	/sys/devices/system/node/nodeX/arch/sgx_size
	/sys/devices/system/node/nodeX/x86/sgx_size
	/sys/devices/system/node/nodeX/coco/sgx_size

There's somebody else *today* who is trying to do something in the same
general area: per-node platform-specific memory encryption capabilities:

> https://lore.kernel.org/all/20211027195511.207552-6-martin.fernandez@eclypsium.com/

Also, could we please think through how this will look if we add more
attributes?  I can imagine wanting both:

	* total SGX memory available
	* total SGX memory present

But those would be quite hard to differentiate if we have just an
"sgx_size".

Wouldn't it be much nicer to name them things like:

	sgx_present_bytes
	sgx_available_bytes

?

In other words, can we please try to think just a bit into the future on
this one?  What other SGX things will we want to export like this?
Outside of SGX, who else wants stuff _like_ this?