linux-kernel - Re: [PATCH v3 2/2] x86/sgx: Add SGX

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Date:   Wed, 01 Sep 2021 04:51:31 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>, linux-sgx@...r.kernel.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>,
        Jonathan Corbet <corbet@....net>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 2/2] x86/sgx: Add SGX_MemTotal to /proc/meminfo

On Thu, 2021-08-26 at 15:27 -0700, Randy Dunlap wrote:
> On 8/26/21 1:27 PM, Dave Hansen wrote:
> > On 8/26/21 9:17 AM, Jarkko Sakkinen wrote:
> > > > I would prefer to see this listed in Documentation/filesystems/proc.rst
> > > > as an optional field, depending on CONFIG_X86_SGX.
> > > > Or at least put a reference in proc.rst to this doc file and its
> > > > supplemental fields.
> > > > 
> > > > thanks.
> > > I *can* put it there but I did have reason not to, i.e. these attributes
> > > are neither there:
> > > 
> > > DirectMap4k:     3930904 kB
> > > DirectMap2M:    29440000 kB
> > > DirectMap1G:     1048576 kB
> > > 
> > > And they are implemented in arch specific code.
> > > 
> > > Actually they are undocumented, e.g.
> > > 
> > > $ git grep DirectMap4k
> > > arch/powerpc/mm/book3s64/pgtable.c:     seq_printf(m, "DirectMap4k:    %8lu kB\n",
> > > arch/s390/mm/pageattr.c:        seq_printf(m, "DirectMap4k:    %8lu kB\n",
> > > arch/x86/mm/pat/set_memory.c:   seq_printf(m, "DirectMap4k:    %8lu kB\n",
> > 
> > Yeah, we need to add some arch-specific sections to the documentation.
> > That *could* just be a reference over to a new file:
> > 
> > 	Documentation/x86/meminfo.rst
> > 
> > along with whatever other arches provide their own fields too.
> > 
> 
> Yes, either way works. Thanks.

I'm wondering why /sys/devices/system/node/nodeX/meminfo is not
documented?  At least I could not find its documentation anywhere.

It would actually make more sense not to add anything at all
/proc/meminfo but rather add SGX_MemTotal to
/sys/devices/system/node/nodeX/meminfo because it is easy enough for
user space to calculate the final value. It's just a sum of constants
(no races).

Given the per-node granularity, maybe the arch-specific documentation
should be in Documentation/x86/node-meminfo.rst?

So I'm thinking to drop /proc/meminfo change and report SGX stats only
per-node.

/Jarkko