linux-kernel - Re: [PATCH v5 01/14] iommu: Add dma ownership management interfaces

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Date:   Thu, 6 Jan 2022 11:54:06 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     baolu.lu@...ux.intel.com, Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/14] iommu: Add dma ownership management interfaces

On 1/5/22 3:23 AM, Jason Gunthorpe wrote:
>>>> The device driver oriented interfaces are,
>>>>
>>>> 	int iommu_device_use_dma_api(struct device *dev);
>>>> 	void iommu_device_unuse_dma_api(struct device *dev);
>> Nit, do we care whether it uses the actual DMA API?  Or is it just
>> that iommu_device_use_dma_api() tells us the driver may program the
>> device to do DMA?
> As the main purpose, yes this is all about the DMA API because it
> asserts the group domain is the DMA API's domain.
> 
> There is a secondary purpose that has to do with the user/kernel
> attack you mentioned above. Maintaining the DMA API domain also
> prevents VFIO from allowing userspace to operate any device in the
> group which blocks P2P attacks to MMIO of other devices.
> 
> This is why, even if the driver doesn't use DMA, it should still do a
> iommu_device_use_dma_api(), except in the special cases where we don't
> care about P2P attacks (eg pci-stub, bridges, etc).
> 

By the way, use_dma_api seems hard to read. How about

	iommu_device_use_default_dma()?

Best regards,
baolu