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

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Date:   Wed, 5 Sep 2018 20:36:06 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.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 Tue, Sep 04, 2018 at 11:17:35AM -0700, Sean Christopherson wrote:
> On Tue, Sep 04, 2018 at 09:01:15PM +0300, Andy Shevchenko wrote:
> > On Tue, Sep 4, 2018 a> +/**
> > 
> > > > > +       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.
> > 
> > Why?
> > Does it related to *any* I/O?
> 
> No, hence my other comment that __private or a new tag altogether may
> be more appropriate.  The noderef attribute is what we truly care
> about.

My proposal is that we go with memremap() and use

#define __sgx_epc __attribute__((noderef))

It makes sense to check that direct EPC pointers are not passed to
functions when they are not supposed to.

/Jarkko