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

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Message-ID: <20210802085257.ia3uloyco4gj7yxp@kernel.org>
Date:   Mon, 2 Aug 2021 11:52:57 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.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 11:44:00AM -0700, Luck, Tony wrote:
> 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.
> 
> I thought xarray was overkill ... and it is ... but it makes the code
> considerably shorter/simpler!
> 
> I think I'm going to go with it. Thanks to Jarkko for the suggestion.

If it makes the code considerably simpler, that in my opinion justifies the
minor size increase.

/Jarkko