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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>,
	Vincent Stehle <Vincent.Stehle@arm.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	"ashok.raj@intel.com" <ashok.raj@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Marc Zyngier <Marc.Zyngier@arm.com>,
	Will Deacon <Will.Deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"Liu, Yi L" <yi.l.liu@intel.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: Wed, 19 Jun 2019 12:44:24 +0100
Message-ID: <138f6a16-d2ee-d7b8-7bfb-ac08b6cfb9da@arm.com> (raw)
In-Reply-To: <20190618171908.76284cd7@jacob-builder>

On 19/06/2019 01:19, Jacob Pan wrote:
>>> I see this as a future extension due to limited testing,   
>>
>> I'm wondering how we deal with:
>> (1) old userspace that won't fill the new private_data field in
>> page_response. A new kernel still has to support it.
>> (2) old kernel that won't recognize the new PRIVATE_DATA flag.
>> Currently iommu_page_response() rejects page responses with unknown
>> flags.
>>
>> I guess we'll need a two-way negotiation, where userspace queries
>> whether the kernel supports the flag (2), and the kernel learns
>> whether it should expect the private data to come back (1).
>>
> I am not sure case (1) exist in that there is no existing user space
> supports PRQ w/o private data. Am I missing something?
> 
> For VT-d emulation, private data is always part of the scalable mode
> PASID capability. If vIOMMU query host supports PASID and scalable
> mode, it will always support private data once PRQ is enabled.

Right if VT-d won't ever support page_response without private data then
I don't think we have to worry about (1).

> So I think we only need to negotiate (2) which should be covered by
> VT-d PASID cap.
> 
>>> perhaps for
>>> now, can you add paddings similar to page request? Make it 64B as
>>> well.  
>>
>> I don't think padding is necessary, because iommu_page_response is
>> sent by userspace to the kernel, unlike iommu_fault which is
>> allocated by userspace and filled by the kernel.
>>
>> Page response looks a lot more like existing VFIO mechanisms, so I
>> suppose we'll wrap the iommu_page_response structure and include an
>> argsz parameter at the top:
>>
>> 	struct vfio_iommu_page_response {
>> 		u32 argsz;
>> 		struct iommu_page_response pr;
>> 	};
>>
>> 	struct vfio_iommu_page_response vpr = {
>> 		.argsz = sizeof(vpr),
>> 		.pr = ...
>> 		...
>> 	};
>>
>> 	ioctl(devfd, VFIO_IOMMU_PAGE_RESPONSE, &vpr);
>>
>> In that case supporting private data can be done by simply appending a
>> field at the end (plus the negotiation above).
>>
> Do you mean at the end of struct vfio_iommu_page_response{}? or at
> the end of that seems struct iommu_page_response{}?
> 
> The consumer of the private data is iommu driver not vfio. So I think
> you want to add the new field at the end of struct iommu_page_response,
> right?

Yes that's what I meant

Thanks,
Jean
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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
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 [this message]
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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