linux-kernel - Re: [PATCH v3 2/7] x86/sgx: Add infrastructure to identify SGX EPC pages

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Date:   Mon, 2 Aug 2021 11:51:10 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/7] x86/sgx: Add infrastructure to identify SGX EPC
 pages

On Fri, Jul 30, 2021 at 09:50:59AM -0700, Dave Hansen wrote:
> On 7/30/21 9:46 AM, Sean Christopherson wrote:
> > Out of curiosity, on multi-socket systems, are EPC sections clustered in a single
> > address range, or are they interleaved with regular RAM?  If they're clustered,
> > you could track the min/max across all sections to optimize the common case that
> > an address isn't in any EPC section.
> 
> They're interleaved on the systems that I've seen:
> 
> 	Socket 0 - RAM
> 	Socket 0 - EPC
> 	Socket 1 - RAM
> 	Socket 1 - EPC
> 
> It would probably be pretty expensive in terms of the physical address
> remapping resources to cluster them.

If they were clustered, wouldn't that also break up our initialization code
for NUMA? It's based on detecting of which NUMA nodes address range is the
given EPC section.

I.e. there should be some meta-data to draw the connection to the correct
NUMA node, if they were clustered (which does not exist).

/Jarkko