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Date: Tue, 28 Sep 2021 21:35:05 +0800 From: Lu Baolu <baolu.lu@...ux.intel.com> To: Jason Gunthorpe <jgg@...dia.com>, "Tian, Kevin" <kevin.tian@...el.com> Cc: baolu.lu@...ux.intel.com, "Liu, Yi L" <yi.l.liu@...el.com>, "alex.williamson@...hat.com" <alex.williamson@...hat.com>, "hch@....de" <hch@....de>, "jasowang@...hat.com" <jasowang@...hat.com>, "joro@...tes.org" <joro@...tes.org>, "jean-philippe@...aro.org" <jean-philippe@...aro.org>, "parav@...lanox.com" <parav@...lanox.com>, "lkml@...ux.net" <lkml@...ux.net>, "pbonzini@...hat.com" <pbonzini@...hat.com>, "lushenming@...wei.com" <lushenming@...wei.com>, "eric.auger@...hat.com" <eric.auger@...hat.com>, "corbet@....net" <corbet@....net>, "Raj, Ashok" <ashok.raj@...el.com>, "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>, "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>, "Jiang, Dave" <dave.jiang@...el.com>, "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>, "kwankhede@...dia.com" <kwankhede@...dia.com>, "robin.murphy@....com" <robin.murphy@....com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>, "dwmw2@...radead.org" <dwmw2@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>, "nicolinc@...dia.com" <nicolinc@...dia.com> Subject: Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma interfaces Hi Jason, On 2021/9/28 19:57, Jason Gunthorpe wrote: > On Tue, Sep 28, 2021 at 07:30:41AM +0000, Tian, Kevin wrote: > >>> Also, don't call it "hint", there is nothing hinty about this, it has >>> definitive functional impacts. >> >> possibly dma_mode (too broad?) or dma_usage > > You just need a flag to specify if the driver manages DMA ownership > itself, or if it requires the driver core to setup kernel ownership > > DMA_OWNER_KERNEL > DMA_OWNER_DRIVER_CONTROLLED > > ? > > There is a bool 'suprress_bind_attrs' already so it could be done like > this: > > bool suppress_bind_attrs:1; > > /* If set the driver must call iommu_XX as the first action in probe() */ > bool suppress_dma_owner:1; > > Which is pretty low cost. Yes. Pretty low cost to fix the BUG_ON() issue. Any kernel-DMA driver binding is blocked if the device's iommu group has been put into user- dma mode. Another issue is, when putting a device into user-dma mode, all devices belonging to the same iommu group shouldn't be bound with a kernel-dma driver. Kevin's prototype checks this by READ_ONCE(dev->driver). This is not lock safe as discussed below, https://lore.kernel.org/linux-iommu/20210927130935.GZ964074@nvidia.com/ Any guidance on this? Best regards, baolu
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