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

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Date:   Mon, 17 Dec 2018 20:01:02 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-sgx@...r.kernel.org, sean.j.christopherson@...el.com,
        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 Mon, Dec 17, 2018 at 09:45:40AM -0800, Dave Hansen wrote:
> > +struct sgx_encl *sgx_encl_alloc(struct sgx_secs *secs)
> > +{
> ...
> > +	kref_init(&encl->refcount);
> > +	INIT_LIST_HEAD(&encl->add_page_reqs);
> > +	INIT_RADIX_TREE(&encl->page_tree, GFP_KERNEL);
> > +	mutex_init(&encl->lock);
> > +	INIT_WORK(&encl->add_page_work, sgx_add_page_worker);
> > +
> > +	encl->mm = current->mm;  <---------------------------------> +	encl->base = secs->base;
> > +	encl->size = secs->size;
> > +	encl->ssaframesize = secs->ssa_frame_size;
> > +	encl->backing = backing;
> > +
> > +	return encl;
> > +}
> 
> How is this OK without taking a reference on the mm?
> 
> I have a feeling a bunch of your bugs with the mmu notifiers and so
> forth are because the refcounting is wrong here.
> 
> Sean's SGX_ENCL_MM_RELEASED would, I think be unnecessary if you just
> take a refcount here and release it when the enclave is destroyed.

Right, atomic_inc(encl->mm->count) here and once when releasing.

The we would not even need the whole mmu notifier in the first place.

/Jarkko