From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: "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: Fri, 7 Jun 2019 11:28:13 +0100 [thread overview]
Message-ID: <dc051424-67d7-02ff-9b8e-0d7a8a4e59eb@arm.com> (raw)
In-Reply-To: <20190606132903.064f7ac4@jacob-builder>
On 06/06/2019 21:29, Jacob Pan wrote:
>>>>>> 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 don't think so, it's the implementation's choice. In general I don't
think devices will have a retry limit, but it doesn't seem like the PCI
spec prevents them from implementing one either. It could be useful to
stop retrying after a certain number of faults, for preventing livelocks
when the OS doesn't fix up the page tables and the device would just
repeat the fault indefinitely.
> 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 do give an invalid response for the old PRG (because of unregistering),
but also for the new one, which has a different address that the guest
might be able to page in and would normally return success.
>>> 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.
Yes I think the damage would always be contained within the misbehaving
software
> 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?
Yes, I'll add that to the fault series
Thanks,
Jean
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next prev parent reply other threads:[~2019-06-07 10:28 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
2019-06-07 7:02 ` Auger Eric
2019-06-07 10:28 ` Jean-Philippe Brucker [this message]
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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