Date:   Fri, 27 Jan 2023 09:59:02 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Baolu Lu <baolu.lu@linux.intel.com>
Cc:     Robin Murphy <robin.murphy@arm.com>, joro@8bytes.org,
        will@kernel.org, hch@lst.de, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/8] iommu: Decouple iommu_present() from bus ops
Message-ID: <Y9PYppHmuSVSqQ62@nvidia.com>
References: <cover.1673978700.git.robin.murphy@arm.com>
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On Fri, Jan 27, 2023 at 09:50:29PM +0800, Baolu Lu wrote:
> On 2023/1/26 22:41, Jason Gunthorpe wrote:
> > On Thu, Jan 26, 2023 at 02:21:29PM +0000, Robin Murphy wrote:
> > 
> > > The "check" is inherent in the fact that it's been called at all. VFIO
> > > noiommu*is*  an IOMMU driver in the sense that it provides a bare minimum of
> > > IOMMU API functionality (i.e. creating groups), sufficient to support
> > > (careful) usage by VFIO drivers. There would not seem to be a legitimate
> > > reason for some*other*  driver to be specifically querying a device while it
> > > is already bound to a VFIO driver (and thus may have a noiommu group).
> > Yes, the devices that VFIO assigns to its internal groups never leak
> > outside VFIO's control during their assignment - ie they are
> > continuously bound to VFIO never another driver.
> > 
> > So no other driver can ever see the internal groups unless it is
> > messing around with devices it is not bound to ????
> 
> Fair enough. I was thinking that probably we could make it like below:
> 
> /**
>  * device_iommu_mapped - Returns true when the device DMA is translated
>  *                       by an IOMMU
>  * @dev: Device to perform the check on
>  */
> static inline bool device_iommu_mapped(struct device *dev)
> {
>         return (dev->iommu && dev->iommu->iommu_dev);
> }
> 
> The iommu probe device code guarantees that dev->iommu->iommu_dev is
> valid only after the IOMMU driver's .probe_device returned successfully.
> 
> Any thoughts?

I find the above much clearer if it can work

Jason