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From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Will Deacon <will@kernel.org>, Cornelia Huck <cohuck@redhat.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 4/4] vfio: Require that devices support DMA cache coherence
Date: Fri, 8 Apr 2022 10:37:12 -0300	[thread overview]
Message-ID: <20220408133712.GY2120790@nvidia.com> (raw)
In-Reply-To: <d6b1c72b-c05e-8bd8-c0cb-38e6c7ccfdb6@arm.com>

On Fri, Apr 08, 2022 at 02:28:02PM +0100, Robin Murphy wrote:

> > > One nit. Is it logistically more reasonable to put this patch before
> > > changing VFIO to always set IOMMU_CACHE?
> > 
> > For bisectability it has to be after
> > 
> >      iommu: Redefine IOMMU_CAP_CACHE_COHERENCY as the cap flag for IOMMU_CACHE
> > 
> > Otherwise Intel iommu will stop working with VFIO
> > 
> > The ordering is OK as is because no IOMMU that works with VFIO cares
> > about IOMMU_CACHE.
> 
> The Arm SMMU drivers do (without it even coherent traffic would be
> downgraded to non-cacheable), but then they also handle
> IOMMU_CAP_CACHE_COHERENCY nonsensically, and it happens to work out since
> AFAIK there aren't (yet) any Arm-based systems where you can reasonably try
> to use VFIO that don't also have hardware-coherent PCI. Thus I don't think
> there's any risk of regression for us here.

Right, I was unclear, I meant 'requires IOMMU_CACHE to be unset to
work with VFIO'

Jason
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WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg@nvidia.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Cornelia Huck <cohuck@redhat.com>,
	David Woodhouse <dwmw2@infradead.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Will Deacon <will@kernel.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 4/4] vfio: Require that devices support DMA cache coherence
Date: Fri, 8 Apr 2022 10:37:12 -0300	[thread overview]
Message-ID: <20220408133712.GY2120790@nvidia.com> (raw)
In-Reply-To: <d6b1c72b-c05e-8bd8-c0cb-38e6c7ccfdb6@arm.com>

On Fri, Apr 08, 2022 at 02:28:02PM +0100, Robin Murphy wrote:

> > > One nit. Is it logistically more reasonable to put this patch before
> > > changing VFIO to always set IOMMU_CACHE?
> > 
> > For bisectability it has to be after
> > 
> >      iommu: Redefine IOMMU_CAP_CACHE_COHERENCY as the cap flag for IOMMU_CACHE
> > 
> > Otherwise Intel iommu will stop working with VFIO
> > 
> > The ordering is OK as is because no IOMMU that works with VFIO cares
> > about IOMMU_CACHE.
> 
> The Arm SMMU drivers do (without it even coherent traffic would be
> downgraded to non-cacheable), but then they also handle
> IOMMU_CAP_CACHE_COHERENCY nonsensically, and it happens to work out since
> AFAIK there aren't (yet) any Arm-based systems where you can reasonably try
> to use VFIO that don't also have hardware-coherent PCI. Thus I don't think
> there's any risk of regression for us here.

Right, I was unclear, I meant 'requires IOMMU_CACHE to be unset to
work with VFIO'

Jason

  reply	other threads:[~2022-04-08 13:37 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-07 15:23 [PATCH v2 0/4] Make the iommu driver no-snoop block feature consistent Jason Gunthorpe via iommu
2022-04-07 15:23 ` Jason Gunthorpe
2022-04-07 15:23 ` [PATCH v2 1/4] iommu: Introduce the domain op enforce_cache_coherency() Jason Gunthorpe via iommu
2022-04-07 15:23   ` Jason Gunthorpe
2022-04-08  8:05   ` Tian, Kevin
2022-04-08  8:05     ` Tian, Kevin
2022-04-09 12:44     ` Lu Baolu
2022-04-09 12:44       ` Lu Baolu
2022-04-11 14:11     ` Jason Gunthorpe via iommu
2022-04-11 14:11       ` Jason Gunthorpe
2022-04-08  8:27   ` Tian, Kevin
2022-04-08  8:27     ` Tian, Kevin
2022-04-07 15:23 ` [PATCH v2 2/4] vfio: Move the Intel no-snoop control off of IOMMU_CACHE Jason Gunthorpe via iommu
2022-04-07 15:23   ` Jason Gunthorpe
2022-04-08  8:16   ` Tian, Kevin
2022-04-08  8:16     ` Tian, Kevin
2022-04-09 12:50     ` Lu Baolu
2022-04-09 12:50       ` Lu Baolu
2022-04-12  7:44       ` Tian, Kevin
2022-04-12  7:44         ` Tian, Kevin
2022-04-12 13:13         ` Lu Baolu
2022-04-12 13:13           ` Lu Baolu
2022-04-12 13:20           ` Jason Gunthorpe via iommu
2022-04-12 13:20             ` Jason Gunthorpe
2022-04-12 23:04             ` Tian, Kevin
2022-04-12 23:04               ` Tian, Kevin
2022-04-13 11:37               ` Lu Baolu
2022-04-13 11:37                 ` Lu Baolu
2022-04-08 15:47   ` Alex Williamson
2022-04-08 15:47     ` Alex Williamson
2022-04-11 14:13     ` Jason Gunthorpe via iommu
2022-04-11 14:13       ` Jason Gunthorpe
2022-04-07 15:23 ` [PATCH v2 3/4] iommu: Redefine IOMMU_CAP_CACHE_COHERENCY as the cap flag for IOMMU_CACHE Jason Gunthorpe via iommu
2022-04-07 15:23   ` Jason Gunthorpe
2022-04-08  8:21   ` Tian, Kevin
2022-04-08  8:21     ` Tian, Kevin
2022-04-08 12:21     ` Jason Gunthorpe via iommu
2022-04-08 12:21       ` Jason Gunthorpe
2022-04-09 12:51   ` Lu Baolu
2022-04-09 12:51     ` Lu Baolu
2022-04-07 15:23 ` [PATCH v2 4/4] vfio: Require that devices support DMA cache coherence Jason Gunthorpe via iommu
2022-04-07 15:23   ` Jason Gunthorpe
2022-04-08  8:26   ` Tian, Kevin
2022-04-08  8:26     ` Tian, Kevin
2022-04-08 12:22     ` Jason Gunthorpe via iommu
2022-04-08 12:22       ` Jason Gunthorpe
2022-04-08 13:28       ` Robin Murphy
2022-04-08 13:28         ` Robin Murphy
2022-04-08 13:37         ` Jason Gunthorpe via iommu [this message]
2022-04-08 13:37           ` Jason Gunthorpe
2022-04-08 15:48   ` Alex Williamson
2022-04-08 15:48     ` Alex Williamson
2022-07-01  4:57   ` Alexey Kardashevskiy
2022-07-01  4:57     ` Alexey Kardashevskiy
2022-07-01  6:07     ` Tian, Kevin
2022-07-01  6:07       ` Tian, Kevin
2022-07-01  6:24       ` Alexey Kardashevskiy
2022-07-01  6:24         ` Alexey Kardashevskiy
2022-04-07 17:03 ` [PATCH v2 0/4] Make the iommu driver no-snoop block feature consistent Robin Murphy
2022-04-07 17:03   ` Robin Murphy
2022-04-07 17:43   ` Jason Gunthorpe via iommu
2022-04-07 17:43     ` Jason Gunthorpe
2022-04-07 18:02     ` Robin Murphy
2022-04-07 18:02       ` Robin Murphy
2022-04-07 19:08       ` Jason Gunthorpe via iommu
2022-04-07 19:08         ` Jason Gunthorpe
2022-04-07 19:27         ` Robin Murphy
2022-04-07 19:27           ` Robin Murphy
2022-04-08 12:18           ` Jason Gunthorpe via iommu
2022-04-08 12:18             ` Jason Gunthorpe
2022-04-08 13:11             ` Robin Murphy
2022-04-08 13:11               ` Robin Murphy
2022-04-08 13:35               ` Jason Gunthorpe via iommu
2022-04-08 13:35                 ` Jason Gunthorpe
2022-04-08 17:44                 ` Robin Murphy
2022-04-08 17:44                   ` Robin Murphy
2022-04-12  2:51                   ` Tian, Kevin
2022-04-12  2:51                     ` Tian, Kevin
2022-04-08  9:08         ` Tian, Kevin
2022-04-08  9:08           ` Tian, Kevin
2022-04-08 10:11           ` Robin Murphy
2022-04-08 10:11             ` Robin Murphy
2022-04-12  2:49             ` Tian, Kevin
2022-04-12  2:49               ` Tian, Kevin

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