linux-kernel - RE: [PATCH v6 12/12] iommu: Improve iopf_queue_flush

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Message-ID: <BN9PR11MB5276018DE2AC15B3538BBC008CC1A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Thu, 28 Sep 2023 05:00:15 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Will Deacon" <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Jason Gunthorpe" <jgg@...pe.ca>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v6 12/12] iommu: Improve iopf_queue_flush_dev()

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Thursday, September 28, 2023 12:28 PM
> 
> The iopf_queue_flush_dev() is called by the iommu driver before releasing
> a PASID. It ensures that all pending faults for this PASID have been
> handled or cancelled, and won't hit the address space that reuses this
> PASID. The driver must make sure that no new fault is added to the queue.
> 
> The SMMUv3 driver doesn't use it because it only implements the
> Arm-specific stall fault model where DMA transactions are held in the SMMU
> while waiting for the OS to handle iopf's. Since a device driver must
> complete all DMA transactions before detaching domain, there are no
> pending iopf's with the stall model. PRI support requires adding a call to
> iopf_queue_flush_dev() after flushing the hardware page fault queue.
> 
> The current implementation of iopf_queue_flush_dev() is a simplified
> version. It is only suitable for SVA case in which the processing of iopf
> is implemented in the inner loop of the iommu subsystem.
> 
> Improve this interface to make it also work for handling iopf out of the
> iommu core. Rename the function with a more meaningful name. Remove a
> warning message in iommu_page_response() since the iopf queue might get
> flushed before possible pending responses.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

Reviewed-by: Kevin Tian <kevin.tian@...el.com>