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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: x86@kernel.org, linux-sgx@vger.kernel.org,
	akpm@linux-foundation.org, dave.hansen@intel.com,
	nhorman@redhat.com, npmccallum@redhat.com, serge.ayoun@intel.com,
	shay.katz-zamir@intel.com, haitao.huang@intel.com,
	andriy.shevchenko@linux.intel.com, tglx@linutronix.de,
	kai.svahn@intel.com, bp@alien8.de, josh@joshtriplett.org,
	luto@kernel.org, kai.huang@intel.com, rientjes@google.com,
	Suresh Siddha <suresh.b.siddha@intel.com>
Subject: Re: [PATCH v19 16/27] x86/sgx: Add the Linux SGX Enclave Driver
Date: Thu, 21 Mar 2019 09:47:14 -0700
Message-ID: <20190321164714.GE6519@linux.intel.com> (raw)
In-Reply-To: <20190321155111.GR4603@linux.intel.com>

On Thu, Mar 21, 2019 at 05:51:11PM +0200, Jarkko Sakkinen wrote:
> On Tue, Mar 19, 2019 at 02:19:51PM -0700, Sean Christopherson wrote:
> > IMO we should get rid of SGX_POWER_LOST_ENCLAVE and the SUSPEND flag.
> > 
> >   - Userspace needs to handle -EFAULT cleanly even if we hook into
> >     suspend/hibernate via sgx_encl_pm_notifier(), e.g. to handle virtual
> >     machine migration.
> >   - In the event that suspend is canceled after sgx_encl_pm_notifier()
> >     runs, we'll have prematurely invalidated the enclave.
> >   - Invalidating all enclaves could be slow on a system with GBs of EPC,
> >     i.e. probably not the best thing to do in the suspend path.
> > 
> > Removing SGX_POWER_LOST_ENCLAVE means we can drop all of the pm_notifier()
> > code, which will likely save us a bit of maintenance down the line.
> 
> I don't disgree. Isn't it a racy flag in the VM context i.e. because
> suspend can happen without SGX core noticing it (running inside a VM)?
> That would a bug.


...

> > > +#ifdef CONFIG_ACPI
> > > +static struct acpi_device_id sgx_device_ids[] = {
> > > +	{"INT0E0C", 0},
> > > +	{"", 0},
> > > +};
> > > +MODULE_DEVICE_TABLE(acpi, sgx_device_ids);
> > > +#endif
> > > +
> > > +static struct platform_driver sgx_drv = {
> > > +	.probe = sgx_drv_probe,
> > > +	.remove = sgx_drv_remove,
> > > +	.driver = {
> > > +		.name			= "sgx",
> > > +		.acpi_match_table	= ACPI_PTR(sgx_device_ids),
> > > +	},
> > > +};
> > 
> > Utilizing the platform driver is unnecessary, adds complexity and IMO is
> > flat out wrong given the current direction of implementing SGX as a
> > full-blooded architectural feature.
> > 
> >   - All hardware information is readily available via CPUID
> >   - arch_initcall hooks obviates the need for ACPI autoprobe
> >   - EPC manager assumes it has full control over all EPC, i.e. EPC
> >     sections are not managed as independent "devices"
> >   - BIOS will enumerate a single ACPI entry regardless of the number
> >     of EPC sections, i.e. the ACPI entry is *only* useful for probing
> >   - Userspace driver matches the EPC device, but doesn't actually
> >     "own" the EPC
> 
> It is for hotplugging. I don't really have strong opinions of this but
> having a driver for uapi allows things like blacklisting sgx.

Hotplugging what?  EPC can't be hotplugged, EPC enumeration through CPUID
won't change post-boot and the ACPI entry can't be relied upon for EPC
base/size information when there are multiple EPC sections.

> > > +
> > > +static int __init sgx_drv_subsys_init(void)
> > > +{
> > > +     int ret;
> > > +
> > > +     ret = bus_register(&sgx_bus_type);
> > 
> > Do we really need a bus/class?  Allocating a chrdev region also seems like
> > overkill.  At this point there is exactly one SGX device, and while there
> > is a pretty good chance we'll end up with a virtualization specific device
> > for exposing EPC to guest, there's no guarantee said device will be SGX
> > specific.  Using a dynamic miscdevice would eliminate a big chunk of code.
> 
> AFAIK misc is not recommended for any new drivers as it has suvere
> limitations like not allowing to add non-racy sysfs attributes. Whatever
> the solution is, lets not use misc.

Ah right, forgot about that.

> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	ret = alloc_chrdev_region(&sgx_devt, 0, SGX_DRV_NR_DEVICES, "sgx");
> > > +	if (ret < 0) {
> > > +		bus_unregister(&sgx_bus_type);
> > > +		return ret;
> > > +	}
> > > +
> > > +	return 0;
> > > +}

...

> > > +static void sgx_vma_open(struct vm_area_struct *vma)
> > > +{
> > > +	struct sgx_encl *encl = vma->vm_private_data;
> > > +	struct sgx_encl_mm *mm;
> > > +
> > > +	if (!encl)
> > > +		return;
> > > +
> > > +	if (encl->flags & SGX_ENCL_DEAD)
> > > +		goto out;
> > > +
> > > +	mm = sgx_encl_get_mm(encl, vma->vm_mm);
> > > +	if (!mm) {
> > > +		mm = kzalloc(sizeof(*mm), GFP_KERNEL);
> > > +		if (!mm) {
> > > +			encl->flags |= SGX_ENCL_DEAD;
> > 
> > Failure to allocate memory for one user of the enclave shouldn't kill
> > the enclave, e.g. failing during fork() shouldn't kill the enclave in
> > the the parent.  And marking an enclave dead without holding its lock
> > is all kinds of bad.
> 
> This is almost non-existent occasion. Agree with the locking though..
> And I'm open for other fallbacks but given the rarity I think the
> current one in sustainable.

What if we clear vm_private_data?  And maybe do a pr_warn_ratelimited()
so that userspace gets some form of notification that forking an enclave
failed.  A NULL encl is easy to check in the fault handler and any where
else we consume vmas.

> 
> > 
> > > +			goto out;
> > > +		}
> > > +
> > > +		spin_lock(&encl->mm_lock);
> > > +		mm->encl = encl;
> > > +		mm->mm = vma->vm_mm;
> > > +		list_add(&mm->list, &encl->mm_list);
> > > +		kref_init(&mm->refcount);
> > 
> > Not that it truly matters, but list_add() is the only thing that needs
> > to be protected with the spinlock, everything else can be done ahead of
> > time.
> 
> True :-)
> 
> > 
> > > +		spin_unlock(&encl->mm_lock);
> > > +	} else {
> > > +		mmdrop(mm->mm);
> > > +	}
> > > +
> > > +out:
> > > +	kref_get(&encl->refcount);
> > > +}
> > > +
> > > +static void sgx_vma_close(struct vm_area_struct *vma)
> > > +{
> > > +	struct sgx_encl *encl = vma->vm_private_data;
> > > +	struct sgx_encl_mm *mm;
> > > +
> > > +	if (!encl)
> > > +		return;
> > > +
> > > +	mm = sgx_encl_get_mm(encl, vma->vm_mm);
> > 
> > Isn't this unnecessary?  sgx_vma_open() had to have been called on this
> > VMA, otherwise we wouldn't be here.
> 
> Not in the case when allocation fails in vma_open.

Ah, I see the flow.  If we do keep the enclave killing behavior then I
think it'd make sense to let this be handled by checking SGX_ENCL_DEAD.
But AFAICT things will "just work" if we nullify vm_private_data.

  reply index

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-17 21:14 [PATCH v19 00/27] Intel SGX1 support Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 01/27] x86/cpufeatures: Add Intel-defined SGX feature bit Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 02/27] x86/cpufeatures: Add SGX sub-features (as Linux-defined bits) Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 03/27] x86/msr: Add IA32_FEATURE_CONTROL.SGX_ENABLE definition Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 04/27] x86/cpufeatures: Add Intel-defined SGX_LC feature bit Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 05/27] x86/msr: Add SGX Launch Control MSR definitions Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 06/27] x86/mm: x86/sgx: Add new 'PF_SGX' page fault error code bit Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 07/27] x86/mm: x86/sgx: Signal SIGSEGV for userspace #PFs w/ PF_SGX Jarkko Sakkinen
2019-03-18 17:15   ` Dave Hansen
2019-03-18 19:53     ` Sean Christopherson
2019-03-17 21:14 ` [PATCH v19 08/27] x86/cpu/intel: Detect SGX support and update caps appropriately Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 09/27] x86/sgx: Add ENCLS architectural error codes Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 10/27] x86/sgx: Add SGX1 and SGX2 architectural data structures Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 11/27] x86/sgx: Add definitions for SGX's CPUID leaf and variable sub-leafs Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 12/27] x86/sgx: Enumerate and track EPC sections Jarkko Sakkinen
2019-03-18 19:50   ` Sean Christopherson
2019-03-21 14:40     ` Jarkko Sakkinen
2019-03-21 15:28       ` Sean Christopherson
2019-03-22 10:19         ` Jarkko Sakkinen
2019-03-22 10:50           ` Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 13/27] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen
2019-03-19 19:59   ` Sean Christopherson
2019-03-21 14:51     ` Jarkko Sakkinen
2019-03-21 15:40       ` Sean Christopherson
2019-03-22 11:00         ` Jarkko Sakkinen
2019-03-22 16:43           ` Sean Christopherson
2019-03-17 21:14 ` [PATCH v19 16/27] x86/sgx: Add the Linux SGX Enclave Driver Jarkko Sakkinen
2019-03-19 21:19   ` Sean Christopherson
2019-03-21 15:51     ` Jarkko Sakkinen
2019-03-21 16:47       ` Sean Christopherson [this message]
2019-03-22 11:10         ` Jarkko Sakkinen
2019-03-26 13:26       ` Jarkko Sakkinen
2019-03-26 23:58         ` Sean Christopherson
2019-03-27  5:28           ` Jarkko Sakkinen
2019-03-27 17:57             ` Sean Christopherson
2019-03-27 18:38             ` Jethro Beekman
2019-03-27 20:06               ` Sean Christopherson
2019-03-28  1:21                 ` Jethro Beekman
2019-03-28 13:19                 ` Jarkko Sakkinen
2019-03-28 19:05                   ` Andy Lutomirski
2019-03-29  9:43                     ` Jarkko Sakkinen
2019-03-29 16:20                     ` Sean Christopherson
2019-04-01 10:01                       ` Jarkko Sakkinen
2019-04-01 17:25                         ` Jethro Beekman
2019-04-01 22:57                           ` Jarkko Sakkinen
2019-03-28 13:15               ` Jarkko Sakkinen
2019-03-19 23:00   ` Sean Christopherson
2019-03-21 16:18     ` Jarkko Sakkinen
2019-03-21 17:38       ` Sean Christopherson
2019-03-22 11:17         ` Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 17/27] x86/sgx: Add provisioning Jarkko Sakkinen
2019-03-19 20:09   ` Sean Christopherson
2019-03-21  2:08     ` Huang, Kai
2019-03-21 14:32       ` Jarkko Sakkinen
2019-03-21 21:41         ` Huang, Kai
2019-03-22 11:31           ` Jarkko Sakkinen
2019-03-21 14:30     ` Jarkko Sakkinen
2019-03-21 14:38   ` Nathaniel McCallum
2019-03-22 11:22     ` Jarkko Sakkinen
2019-03-21 16:50   ` Andy Lutomirski
2019-03-22 11:29     ` Jarkko Sakkinen
2019-03-22 11:43       ` Jarkko Sakkinen
2019-03-22 18:20         ` Andy Lutomirski
2019-03-25 14:55           ` Jarkko Sakkinen
2019-03-27  0:14             ` Sean Christopherson
2019-04-05 10:18             ` Jarkko Sakkinen
2019-04-05 13:53               ` Andy Lutomirski
2019-04-05 14:20                 ` Jarkko Sakkinen
2019-04-05 14:34                   ` Greg KH
2019-04-09 13:37                     ` Jarkko Sakkinen
2019-04-05 14:21                 ` Greg KH
2019-03-17 21:14 ` [PATCH v19 19/27] x86/sgx: ptrace() support for the SGX driver Jarkko Sakkinen
2019-03-19 22:22   ` Sean Christopherson
2019-03-21 15:02     ` Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 20/27] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 21/27] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 22/27] x86/fault: Attempt to fixup unhandled #PF in vDSO before signaling Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 23/27] x86/traps: Attempt to fixup exceptions " Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 25/27] x86/sgx: SGX documentation Jarkko Sakkinen
2019-03-20 17:14   ` Sean Christopherson
2019-03-21 16:24     ` Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 26/27] selftests/x86: Add a selftest for SGX Jarkko Sakkinen
2019-03-17 21:14 ` [PATCH v19 27/27] x86/sgx: Update MAINTAINERS Jarkko Sakkinen
2019-03-19 17:12   ` Sean Christopherson
2019-03-21 14:42     ` Jarkko Sakkinen
     [not found] ` <20190317211456.13927-19-jarkko.sakkinen@linux.intel.com>
2019-03-19 22:09   ` [PATCH v19 18/27] x86/sgx: Add swapping code to the core and SGX driver Sean Christopherson
2019-03-21 14:59     ` Jarkko Sakkinen
2019-03-19 23:41 ` [PATCH v19 00/27] Intel SGX1 support Sean Christopherson
2019-03-19 23:52   ` Jethro Beekman
2019-03-20  0:22     ` Sean Christopherson
2019-03-21 16:20     ` Jarkko Sakkinen
2019-03-21 16:00   ` Jarkko Sakkinen

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