linux-kernel - Re: [intel-sgx-kernel-dev] [PATCH v7 4/8] intel_sgx: driver for Intel Software Guard Extensions

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Message-ID: <20171214124256.muofgcwiz4js454p@linux.intel.com>
Date:   Thu, 14 Dec 2017 14:42:56 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>
Cc:     "intel-sgx-kernel-dev@...ts.01.org" 
        <intel-sgx-kernel-dev@...ts.01.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Shevchenko <andy@...radead.org>
Subject: Re: [intel-sgx-kernel-dev] [PATCH v7 4/8] intel_sgx: driver for
 Intel Software Guard Extensions

On Fri, Dec 08, 2017 at 03:31:38PM +0000, Christopherson, Sean J wrote:
> Three VA pages in the enclave: A, B and C.  Evict all pages in the
> enclave, i.e. consume all slots in A, B and C.  The list can be in
> any order at this point, but for the sake of argument let's say the
> order is C->A->B, i.e. C was originally the last VA page in the list.
> Fault in page X, whose VA is in B.  Evict X.  This code looks at C
> and A, and finds no available slot, but continues with VA page A and
> a va_offset of PAGE_SIZE.


#PF handler moves B to the beginning of list when X if faulted so the
list would be at that point

B->C->A

And thus C would get VA slot from B.

/Jarkko