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

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Date:   Mon, 17 Dec 2018 11:40:18 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-sgx@...r.kernel.org, nhorman@...hat.com,
        npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        kai.svahn@...el.com, mark.shanahan@...el.com, luto@...capital.net,
        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>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

On 12/17/18 11:37 AM, Jarkko Sakkinen wrote:
>> Suggestion:
>>
>> It looks like you only expect one VMA per enclave.  Things go bonkers if
>> this is not true.  So, instead of storing encl->mm, don't.  You can get
>> the mm from vma->vm_mm and you could just store encl->vma instead.
> The code actually supports having multiple VMAs per enclave.

That seems at least somewhat at odds with this comment:

> static void sgx_vma_open(struct vm_area_struct *vma)
> {
>         struct sgx_encl *encl = vma->vm_private_data;
> 
>         if (!encl)
>                 return;
> 
>         /* kref cannot underflow because ECREATE ioctl checks that there is only
>          * one single VMA for the enclave before proceeding.
>          */
>         kref_get(&encl->refcount);
> }