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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Date:   Sun, 31 Oct 2021 19:49:21 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>,
        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 Fri, 2021-10-29 at 10:00 -0700, Dave Hansen wrote:
> 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

Sure, I can rename the attribute group as "x86".

> 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/

Martin's is adding a new attribute as part of pre-existing attribute group for
node device, where as my patch is adding a completely new named attribute
group.

> 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?

I don't mind renaming the attribute but maybe it should sgx_total_bytes, just
because in some other sysfs attributes that keyword is used to refer all of the
bytes?

/Jarkko