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From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Cc: jacob.jun.pan@linux.intel.com,
	"kevin.tian@intel.com" <kevin.tian@intel.com>,
	"yi.l.liu@intel.com" <yi.l.liu@intel.com>,
	"ashok.raj@intel.com" <ashok.raj@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Marc Zyngier <Marc.Zyngier@arm.com>,
	"joro@8bytes.org" <joro@8bytes.org>,
	Will Deacon <Will.Deacon@arm.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Vincent Stehle <Vincent.Stehle@arm.com>,
	Robin Murphy <Robin.Murphy@arm.com>,
	"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
	"eric.auger.pro@gmail.com" <eric.auger.pro@gmail.com>
Subject: Re: [PATCH v8 26/29] vfio-pci: Register an iommu fault handler
Date: Thu, 6 Jun 2019 13:29:03 -0700	[thread overview]
Message-ID: <20190606132903.064f7ac4@jacob-builder> (raw)
In-Reply-To: <2753d192-1c46-d78e-c425-0c828e48cde2@arm.com>

On Thu, 6 Jun 2019 19:54:05 +0100
Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:

> On 05/06/2019 23:45, Jacob Pan wrote:
> > On Tue, 4 Jun 2019 18:11:08 +0200
> > Auger Eric <eric.auger@redhat.com> wrote:
> >   
> >> Hi Alex,
> >>
> >> On 6/4/19 12:31 AM, Alex Williamson wrote:  
> >>> On Sun, 26 May 2019 18:10:01 +0200
> >>> Eric Auger <eric.auger@redhat.com> wrote:
> >>>     
> >>>> This patch registers a fault handler which records faults in
> >>>> a circular buffer and then signals an eventfd. This buffer is
> >>>> exposed within the fault region.
> >>>>
> >>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> >>>>
> >>>> ---
> >>>>
> >>>> v3 -> v4:
> >>>> - move iommu_unregister_device_fault_handler to vfio_pci_release
> >>>> ---
> >>>>  drivers/vfio/pci/vfio_pci.c         | 49
> >>>> +++++++++++++++++++++++++++++ drivers/vfio/pci/vfio_pci_private.h
> >>>> |  1 + 2 files changed, 50 insertions(+)
> >>>>
> >>>> diff --git a/drivers/vfio/pci/vfio_pci.c
> >>>> b/drivers/vfio/pci/vfio_pci.c index f75f61127277..520999994ba8
> >>>> 100644 --- a/drivers/vfio/pci/vfio_pci.c
> >>>> +++ b/drivers/vfio/pci/vfio_pci.c
> >>>> @@ -30,6 +30,7 @@
> >>>>  #include <linux/vfio.h>
> >>>>  #include <linux/vgaarb.h>
> >>>>  #include <linux/nospec.h>
> >>>> +#include <linux/circ_buf.h>
> >>>>  
> >>>>  #include "vfio_pci_private.h"
> >>>>  
> >>>> @@ -296,6 +297,46 @@ static const struct vfio_pci_regops
> >>>> vfio_pci_fault_prod_regops = { .add_capability =
> >>>> vfio_pci_fault_prod_add_capability, };
> >>>>  
> >>>> +int vfio_pci_iommu_dev_fault_handler(struct iommu_fault_event
> >>>> *evt, void *data) +{
> >>>> +	struct vfio_pci_device *vdev = (struct vfio_pci_device
> >>>> *) data;
> >>>> +	struct vfio_region_fault_prod *prod_region =
> >>>> +		(struct vfio_region_fault_prod
> >>>> *)vdev->fault_pages;
> >>>> +	struct vfio_region_fault_cons *cons_region =
> >>>> +		(struct vfio_region_fault_cons
> >>>> *)(vdev->fault_pages + 2 * PAGE_SIZE);
> >>>> +	struct iommu_fault *new =
> >>>> +		(struct iommu_fault *)(vdev->fault_pages +
> >>>> prod_region->offset +
> >>>> +			prod_region->prod *
> >>>> prod_region->entry_size);
> >>>> +	int prod, cons, size;
> >>>> +
> >>>> +	mutex_lock(&vdev->fault_queue_lock);
> >>>> +
> >>>> +	if (!vdev->fault_abi)
> >>>> +		goto unlock;
> >>>> +
> >>>> +	prod = prod_region->prod;
> >>>> +	cons = cons_region->cons;
> >>>> +	size = prod_region->nb_entries;
> >>>> +
> >>>> +	if (CIRC_SPACE(prod, cons, size) < 1)
> >>>> +		goto unlock;
> >>>> +
> >>>> +	*new = evt->fault;
> >>>> +	prod = (prod + 1) % size;
> >>>> +	prod_region->prod = prod;
> >>>> +	mutex_unlock(&vdev->fault_queue_lock);
> >>>> +
> >>>> +	mutex_lock(&vdev->igate);
> >>>> +	if (vdev->dma_fault_trigger)
> >>>> +		eventfd_signal(vdev->dma_fault_trigger, 1);
> >>>> +	mutex_unlock(&vdev->igate);
> >>>> +	return 0;
> >>>> +
> >>>> +unlock:
> >>>> +	mutex_unlock(&vdev->fault_queue_lock);
> >>>> +	return -EINVAL;
> >>>> +}
> >>>> +
> >>>>  static int vfio_pci_init_fault_region(struct vfio_pci_device
> >>>> *vdev) {
> >>>>  	struct vfio_region_fault_prod *header;
> >>>> @@ -328,6 +369,13 @@ static int vfio_pci_init_fault_region(struct
> >>>> vfio_pci_device *vdev) header = (struct vfio_region_fault_prod
> >>>> *)vdev->fault_pages; header->version = -1;
> >>>>  	header->offset = PAGE_SIZE;
> >>>> +
> >>>> +	ret =
> >>>> iommu_register_device_fault_handler(&vdev->pdev->dev,
> >>>> +
> >>>> vfio_pci_iommu_dev_fault_handler,
> >>>> +					vdev);
> >>>> +	if (ret)
> >>>> +		goto out;
> >>>> +
> >>>>  	return 0;
> >>>>  out:
> >>>>  	kfree(vdev->fault_pages);
> >>>> @@ -570,6 +618,7 @@ static void vfio_pci_release(void
> >>>> *device_data) if (!(--vdev->refcnt)) {
> >>>>  		vfio_spapr_pci_eeh_release(vdev->pdev);
> >>>>  		vfio_pci_disable(vdev);
> >>>> +
> >>>> iommu_unregister_device_fault_handler(&vdev->pdev->dev);    
> >>>
> >>>
> >>> But this can fail if there are pending faults which leaves a
> >>> device reference and then the system is broken :(    
> >> This series only features unrecoverable errors and for those the
> >> unregistration cannot fail. Now unrecoverable errors were added I
> >> admit this is confusing. We need to sort this out or clean the
> >> dependencies.  
> > As Alex pointed out in 4/29, we can make
> > iommu_unregister_device_fault_handler() never fail and clean up all
> > the pending faults in the host IOMMU belong to that device. But the
> > problem is that if a fault, such as PRQ, has already been injected
> > into the guest, the page response may come back after handler is
> > unregistered and registered again.  
> 
> I'm trying to figure out if that would be harmful in any way. I guess
> it can be a bit nasty if we handle the page response right after
> having injected a new page request that uses the same PRGI. In any
> other case we discard the page response, but here we forward it to
> the endpoint and:
> 
> * If the response status is success, endpoint retries the
> translation. The guest probably hasn't had time to handle the new
> page request and translation will fail, which may lead the endpoint
> to give up (two unsuccessful translation requests). Or send a new
> request
> 
Good point, there shouldn't be any harm if the page response is a
"fake" success. In fact it could happen in the normal operation when
PRQs to two devices share the same non-leaf translation structure. The
worst case is just a retry. I am not aware of the retry limit, is it in
the PCIe spec? I cannot find it.

I think we should just document it, similar to having a spurious
interrupt. The PRQ trace event should capture that as well.

> * otherwise the endpoint won't retry the access, and could also
> disable PRI if the status is failure.
> 
That would be true regardless this race condition with handler
registration. So should be fine.

> > We need a way to reject such page response belong
> > to the previous life of the handler. Perhaps a sync call to the
> > guest with your fault queue eventfd? I am not sure.  
> 
> We could simply expect the device driver not to send any page response
> after unregistering the fault handler. Is there any reason VFIO would
> need to unregister and re-register the fault handler on a live guest?
> 
There is no reason for VFIO to unregister and register again, I was
just thinking from security perspective. Someone could write a VFIO app
do this attack. But I agree the damage is within the device, may get
PRI disabled as a result.

So it seems we agree on the following:
- iommu_unregister_device_fault_handler() will never fail
- iommu driver cleans up all pending faults when handler is unregistered
- assume device driver or guest not sending more page response _after_
  handler is unregistered.
- system will tolerate rare spurious response

Sounds right?

> Thanks,
> Jean

[Jacob Pan]
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  reply	other threads:[~2019-06-06 20:26 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-26 16:09 [PATCH v8 00/29] SMMUv3 Nested Stage Setup Eric Auger
2019-05-26 16:09 ` [PATCH v8 01/29] driver core: Add per device iommu param Eric Auger
2019-05-26 16:09 ` [PATCH v8 02/29] iommu: Introduce device fault data Eric Auger
2019-05-26 16:09 ` [PATCH v8 03/29] iommu: Introduce device fault report API Eric Auger
2019-05-26 16:09 ` [PATCH v8 04/29] iommu: Add recoverable fault reporting Eric Auger
2019-06-03 22:31   ` Alex Williamson
2019-06-04 15:48     ` Jacob Pan
2019-05-26 16:09 ` [PATCH v8 05/29] iommu: Add a timeout parameter for PRQ response Eric Auger
2019-06-03 22:32   ` Alex Williamson
2019-06-04 10:52     ` Jean-Philippe Brucker
2019-06-04 15:50       ` Jacob Pan
2019-05-26 16:09 ` [PATCH v8 06/29] trace/iommu: Add sva trace events Eric Auger
2019-05-26 16:09 ` [PATCH v8 07/29] iommu: Use device fault trace event Eric Auger
2019-05-26 16:09 ` [PATCH v8 08/29] iommu: Introduce attach/detach_pasid_table API Eric Auger
2019-05-26 16:09 ` [PATCH v8 09/29] iommu: Introduce cache_invalidate API Eric Auger
2019-05-26 16:09 ` [PATCH v8 10/29] iommu: Introduce bind/unbind_guest_msi Eric Auger
2019-05-26 16:09 ` [PATCH v8 11/29] iommu/arm-smmu-v3: Maintain a SID->device structure Eric Auger
2019-05-26 16:09 ` [PATCH v8 12/29] iommu/smmuv3: Dynamically allocate s1_cfg and s2_cfg Eric Auger
2019-05-26 16:09 ` [PATCH v8 13/29] iommu/smmuv3: Get prepared for nested stage support Eric Auger
2019-05-26 16:09 ` [PATCH v8 14/29] iommu/smmuv3: Implement attach/detach_pasid_table Eric Auger
2019-05-26 16:09 ` [PATCH v8 15/29] iommu/smmuv3: Introduce __arm_smmu_tlb_inv_asid/s1_range_nosync Eric Auger
2019-05-26 16:09 ` [PATCH v8 16/29] iommu/smmuv3: Implement cache_invalidate Eric Auger
2019-05-26 16:09 ` [PATCH v8 17/29] dma-iommu: Implement NESTED_MSI cookie Eric Auger
2019-05-26 16:09 ` [PATCH v8 18/29] iommu/smmuv3: Nested mode single MSI doorbell per domain enforcement Eric Auger
2019-05-26 16:09 ` [PATCH v8 19/29] iommu/smmuv3: Enforce incompatibility between nested mode and HW MSI regions Eric Auger
2019-05-26 16:09 ` [PATCH v8 20/29] iommu/smmuv3: Implement bind/unbind_guest_msi Eric Auger
2019-05-26 16:09 ` [PATCH v8 21/29] iommu/smmuv3: Report non recoverable faults Eric Auger
2019-05-26 16:09 ` [PATCH v8 22/29] vfio: VFIO_IOMMU_ATTACH/DETACH_PASID_TABLE Eric Auger
2019-06-03 22:32   ` Alex Williamson
2019-05-26 16:09 ` [PATCH v8 23/29] vfio: VFIO_IOMMU_CACHE_INVALIDATE Eric Auger
2019-06-14 12:38   ` Liu, Yi L
2019-06-14 13:17     ` Auger Eric
2019-05-26 16:09 ` [PATCH v8 24/29] vfio: VFIO_IOMMU_BIND/UNBIND_MSI Eric Auger
2019-06-03 22:32   ` Alex Williamson
2019-06-07  8:30     ` Auger Eric
2019-05-26 16:10 ` [PATCH v8 25/29] vfio-pci: Add a new VFIO_REGION_TYPE_NESTED region type Eric Auger
2019-06-03 22:31   ` Alex Williamson
2019-06-07  8:28     ` Auger Eric
2019-06-07 12:47       ` Jean-Philippe Brucker
2019-06-07 16:29       ` Alex Williamson
2019-05-26 16:10 ` [PATCH v8 26/29] vfio-pci: Register an iommu fault handler Eric Auger
2019-06-03 22:31   ` Alex Williamson
2019-06-04 16:11     ` Auger Eric
2019-06-05 22:45       ` Jacob Pan
2019-06-06 18:54         ` Jean-Philippe Brucker
2019-06-06 20:29           ` Jacob Pan [this message]
2019-06-07  7:02             ` Auger Eric
2019-06-07 10:28             ` Jean-Philippe Brucker
2019-06-07 17:43               ` Jacob Pan
2019-06-10 12:45                 ` Jean-Philippe Brucker
2019-06-10 21:31                   ` Jacob Pan
2019-06-11 13:14                     ` Jean-Philippe Brucker
2019-06-12 18:53                       ` Jacob Pan
2019-06-18 14:04                         ` Jean-Philippe Brucker
2019-06-19  0:19                           ` Jacob Pan
2019-06-19 11:44                             ` Jean-Philippe Brucker
2019-07-11 13:07                           ` Auger Eric
2019-06-07 12:48   ` Jean-Philippe Brucker
2019-06-07 14:18     ` Auger Eric
2019-05-26 16:10 ` [PATCH v8 27/29] vfio_pci: Allow to mmap the fault queue Eric Auger
2019-05-26 16:10 ` [PATCH v8 28/29] vfio-pci: Add VFIO_PCI_DMA_FAULT_IRQ_INDEX Eric Auger
2019-06-03 22:31   ` Alex Williamson
2019-06-04 16:11     ` Auger Eric
2019-05-26 16:10 ` [PATCH v8 29/29] vfio: Document nested stage control Eric Auger

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