linux-kernel - Re: [PATCH 1/8] iommu: Decouple iommu

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Message-ID: <b6b55688-1390-4e92-8184-770154a8955d@linux.intel.com>
Date:   Fri, 27 Jan 2023 21:50:29 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     baolu.lu@...ux.intel.com, joro@...tes.org, will@...nel.org,
        hch@....de, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] iommu: Decouple iommu_present() from bus ops

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?

Best regards,
baolu