linux-kernel - Re: [PATCH v2 02/17] driver core: Add dma_unconfigure callback in bus

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Message-ID: <YaM3slBGozqxsQ+m@kroah.com>
Date:   Sun, 28 Nov 2021 09:02:58 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        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>, iommu@...ts.linux-foundation.org,
        linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/17] driver core: Add dma_unconfigure callback in
 bus_type

On Sun, Nov 28, 2021 at 10:50:36AM +0800, Lu Baolu wrote:
> The bus_type structure defines dma_configure() callback for bus drivers
> to configure DMA on the devices. This adds the paired dma_unconfigure()
> callback and calls it during driver unbinding so that bus drivers can do
> some cleanup work.
> 
> One use case for this paired DMA callbacks is for the bus driver to check
> for DMA ownership conflicts during driver binding, where multiple devices
> belonging to a same IOMMU group (the minimum granularity of isolation and
> protection) may be assigned to kernel drivers or user space respectively.
> 
> Without this change, for example, the vfio driver has to listen to a bus
> BOUND_DRIVER event and then BUG_ON() in case of dma ownership conflict.
> This leads to bad user experience since careless driver binding operation
> may crash the system if the admin overlooks the group restriction. Aside
> from bad design, this leads to a security problem as a root user, even with
> lockdown=integrity, can force the kernel to BUG.
> 
> With this change, the bus driver could check and set the DMA ownership in
> driver binding process and fail on ownership conflicts. The DMA ownership
> should be released during driver unbinding.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Link: https://lore.kernel.org/linux-iommu/20210922123931.GI327412@nvidia.com/
> Link: https://lore.kernel.org/linux-iommu/20210928115751.GK964074@nvidia.com/
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  include/linux/device/bus.h | 3 +++
>  drivers/base/dd.c          | 7 ++++++-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index a039ab809753..ef54a71e5f8f 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -59,6 +59,8 @@ struct fwnode_handle;
>   *		bus supports.
>   * @dma_configure:	Called to setup DMA configuration on a device on
>   *			this bus.
> + * @dma_unconfigure:	Called to cleanup DMA configuration on a device on
> + *			this bus.

"dma_cleanup()" is a better name for this, don't you think?

thanks,

greg k-h