linux-kernel - Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

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Message-ID: <20181217184625.GE12491@linux.intel.com>
Date:   Mon, 17 Dec 2018 10:46:25 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     "Dr. Greg" <greg@...ellic.com>,
        Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-sgx@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        nhorman@...hat.com, npmccallum@...hat.com,
        "Ayoun, Serge" <serge.ayoun@...el.com>, shay.katz-zamir@...el.com,
        haitao.huang@...ux.intel.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Svahn, Kai" <kai.svahn@...el.com>, mark.shanahan@...el.com,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, jethro@...tanix.com
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

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