linux-kernel - Re: [PATCH v13 07/13] x86/sgx: Add data structures for tracking the EPC pages

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Date:   Tue, 4 Sep 2018 10:49:14 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>, nhorman@...hat.com,
        npmccallum@...hat.com, linux-sgx@...r.kernel.org,
        serge.ayoun@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, suresh.b.siddha@...el.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 07/13] x86/sgx: Add data structures for tracking the
 EPC pages

On Mon, Sep 03, 2018 at 05:41:53PM +0300, Andy Shevchenko wrote:
> On Mon, Aug 27, 2018 at 9:58 PM Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> 
> > +       va = ioremap_cache(addr, size);
> > +       if (!va)
> > +               return -ENOMEM;
> 
> I'm not sure this is a right API. Do we operate with memory? Does it
> have I/O side effects?
> If no, memremap() would be better to use.

Preserving __iomem is desirable.  There aren't side effects per se,
but direct non-enclave accesses to the EPC get abort page semantics so
the kernel shouldn't be directly dereferencing a pointer to the EPC.
Though by that argument, sgx_epc_bank.va, sgx_epc_addr's return and
all ENCLS helpers should be tagged __iomem.

For documentation purposes, maybe it would be better to use __private
or "#define __sgx_epc __iomem" and use that?