linux-kernel - Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF

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Message-Id: <2D60780F-ADB4-48A4-AB74-15683493D369@amacapital.net>
Date:   Wed, 26 Sep 2018 11:12:27 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...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, linux-sgx@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF_SGX


> On Sep 26, 2018, at 10:35 AM, Sean Christopherson <sean.j.christopherson@...el.com> wrote:
> 
>> On Tue, Sep 25, 2018 at 03:53:48PM -0700, Andy Lutomirski wrote:
>> Minor nit:
>> 
>> On Tue, Sep 25, 2018 at 6:12 AM Jarkko Sakkinen
>> <jarkko.sakkinen@...ux.intel.com> wrote:
>>> 
>>> From: Sean Christopherson <sean.j.christopherson@...el.com>
>>> 
>> 
>>> by (c) as the kernel doesn't really have any other reasonable option,
>>> e.g. we could kill the task or panic, but neither is warranted.
>> 
>> Not killing the task is quite nice, but...
>> 
>>> +       /*
>>> +        * Access is blocked by the Enclave Page Cache Map (EPCM),
>>> +        * i.e. the access is allowed by the PTE but not the EPCM.
>>> +        * This usually happens when the EPCM is yanked out from
>>> +        * under us, e.g. by hardware after a suspend/resume cycle.
>>> +        * In any case, there is nothing that can be done by the
>>> +        * kernel to resolve the fault (short of killing the task).
>> 
>> Maybe s/killing the task/sending a signal/?
> 
> My intent was to document that, unlike all other page faults, the
> kernel can't fix the source of the fault even if it were omniscient.
> 
> How about this?  With formatting changes since it's long-winded...
> 
>        /*
>         * Access is blocked by the Enclave Page Cache Map (EPCM), i.e. the
>         * access is allowed by the PTE but not the EPCM.  This usually happens
>         * when the EPCM is yanked out from under us, e.g. by hardware after a
>         * suspend/resume cycle.  In any case, software, i.e. the kernel, can't
>         * fix the source of the fault as the EPCM can't be directly modified
>         * by software.  Handle the fault as an access error in order to signal
>         * userspace, e.g. so that userspace can rebuild their enclave(s), even
>         * though userspace may not have actually violated access permissions.
>         */
> 

Looks good to me.