linux-kernel - Re: [PATCH v15 16/23] x86/sgx: Enumerate and track EPC sections

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Date:   Mon, 5 Nov 2018 19:35:57 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-sgx@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        sean.j.christopherson@...el.com, nhorman@...hat.com,
        npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        mark.shanahan@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        suresh.b.siddha@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v15 16/23] x86/sgx: Enumerate and track EPC sections

On Sat, Nov 03, 2018 at 03:22:34PM +0200, Andy Shevchenko wrote:
> On Sat, Nov 3, 2018 at 1:17 AM Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> >
> > From: Sean Christopherson <sean.j.christopherson@...el.com>
> >
> > Enumerate Enclave Page Cache (EPC) sections via CPUID and add the data
> > structures necessary to track EPC pages so that they can be allocated,
> > freed and managed.  As a system may have multiple EPC sections, invoke
> > CPUID on SGX sub-leafs until an invalid leaf is encountered.
> >
> > On NUMA systems, a node can have at most one bank. A bank can be at
> > most part of two nodes.  SGX supports both nodes with a single memory
> > controller and also sub-cluster nodes with severals memory controllers
> > on a single die.
> >
> > For simplicity, support a maximum of eight EPC sections.  Current
> > client hardware supports only a single section, while upcoming server
> > hardware will support at most eight sections.  Bounding the number of
> > sections also allows the section ID to be embedded along with a page's
> > offset in a single unsigned long, enabling easy retrieval of both the
> > VA and PA for a given page.
> 
> > +       iounmap(section->va);
> 
> > +       section->va = ioremap_cache(addr, size);
> > +       if (!section->va)
> > +               return -ENOMEM;
> 
> I forgot if it's a place in code on which we discussed ioremap() vs.
> memremap() call.
> And I forgot why the conclusion is to leave ioremap().
> 
> Sorry, if I'm mistaken.

Thanks for pointing this out. It very well might I have either

1. forgotten to do the switch.
2. had some open about it that I forgot to ask.

Anyway, I'll check this and at minimum document the reason to the
change log if there is one to keep the ioremap().

/Jarkko