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Fri, 4 Jun 2021 11:58:07 +0000 Received: from BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::3d51:a3b9:8611:684e]) by BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::3d51:a3b9:8611:684e%6]) with mapi id 15.20.4195.024; Fri, 4 Jun 2021 11:58:07 +0000 Date: Fri, 4 Jun 2021 08:58:05 -0300 From: Jason Gunthorpe To: Jason Wang Cc: Alex Williamson , "Tian, Kevin" , Jean-Philippe Brucker , "Jiang, Dave" , "Raj, Ashok" , "kvm@vger.kernel.org" , Jonathan Corbet , Robin Murphy , LKML , "iommu@lists.linux-foundation.org" , David Gibson , Kirti Wankhede , David Woodhouse Subject: Re: [RFC] /dev/ioasid uAPI proposal Message-ID: <20210604115805.GG1002214@nvidia.com> References: <20210602111117.026d4a26.alex.williamson@redhat.com> <20210602173510.GE1002214@nvidia.com> <20210602120111.5e5bcf93.alex.williamson@redhat.com> <20210602180925.GH1002214@nvidia.com> <20210602130053.615db578.alex.williamson@redhat.com> <20210602195404.GI1002214@nvidia.com> <20210602143734.72fb4fa4.alex.williamson@redhat.com> <6a9426d7-ed55-e006-9c4c-6b7c78142e39@redhat.com> <20210603130927.GZ1002214@nvidia.com> <65614634-1db4-7119-1a90-64ba5c6e9042@redhat.com> Content-Type: text/plain; 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I think DMA API should hide > those arch/platform specific stuffs from us. It is not arch/platform stuff. If the device uses no-snoop then a very platform specific recovery is required in the device driver. It is not part of the normal DMA API, it is side APIs like flush_agp_cache() or wbinvd() that are used by GPU drivers only. If drivers/virtio doesn't explicitly call these things it doesn't support no-snoop - hence no VDPA device can ever use no-snoop. Since VIRTIO_F_ACCESS_PLATFORM doesn't trigger wbinvd on x86 it has nothing to do with no-snoop. 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Fri, Jun 04, 2021 at 09:11:03AM +0800, Jason Wang wrote: > > nor do any virtio drivers implement the required platform specific > > cache flushing to make no-snoop TLPs work. > > I don't get why virtio drivers needs to do that. I think DMA API should hide > those arch/platform specific stuffs from us. It is not arch/platform stuff. If the device uses no-snoop then a very platform specific recovery is required in the device driver. It is not part of the normal DMA API, it is side APIs like flush_agp_cache() or wbinvd() that are used by GPU drivers only. If drivers/virtio doesn't explicitly call these things it doesn't support no-snoop - hence no VDPA device can ever use no-snoop. Since VIRTIO_F_ACCESS_PLATFORM doesn't trigger wbinvd on x86 it has nothing to do with no-snoop. Jason _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu