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Date:   Mon, 17 Dec 2018 10:46:25 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     "Dr. Greg" <greg@enjellic.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        Platform Driver <platform-driver-x86@vger.kernel.org>,
        linux-sgx@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
        nhorman@redhat.com, npmccallum@redhat.com,
        "Ayoun, Serge" <serge.ayoun@intel.com>, shay.katz-zamir@intel.com,
        haitao.huang@linux.intel.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Svahn, Kai" <kai.svahn@intel.com>, mark.shanahan@intel.com,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, jethro@fortanix.com
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver
Message-ID: <20181217184625.GE12491@linux.intel.com>
References: <20181212180036.GC6333@linux.intel.com>
 <20181214235917.GA14049@wind.enjellic.com>
 <20181215000627.GA5799@linux.intel.com>
 <20181217132859.GA31936@linux.intel.com>
 <20181217133928.GA32706@linux.intel.com>
 <20181217140811.GA4601@linux.intel.com>
 <20181217173106.GB12491@linux.intel.com>
 <20181217174935.GA12617@linux.intel.com>
 <20181217180957.GC12491@linux.intel.com>
 <20181217182319.GA13288@linux.intel.com>
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On Mon, Dec 17, 2018 at 08:23:19PM +0200, Jarkko Sakkinen wrote:
> On Mon, Dec 17, 2018 at 10:09:57AM -0800, Sean Christopherson wrote:
> > No, EREMOVE should never fail if the enclave is being released, i.e. all
> > references to the enclave are gone.  And failure during sgx_encl_release()
> > means we leaked an EPC page, which warrants a WARN.
> 
> Right that what I was suspecting as swapper should hold a ref to the
> enclave while it is working on it. It is a programming error when this
> happens.
> 
> Maybe change the boolean parameter to flags parameter have a flag to
> use sgx_free_page()?

I tried that approach when I first split it to __sgx_free_page() and
sgx_free_page(), but IMO the code is more difficult to read and harder
to maintain since sgx_free_page() should be used except under special
circumstances, e.g. race with reclaim or the freeing is "untrusted",
i.e. requested by userspace via sgx_ioc_enclave_remove_pages().

> 
> > That makes sense.
> 
> What do you think of Dave's proposal?
> 
> /Jarkko