linux-kernel - RE: [PATCH v2 5/5] iommu/vt-d: Move PRI handling to IOPF feature path

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Date:   Fri, 17 Mar 2023 00:06:05 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
CC:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 5/5] iommu/vt-d: Move PRI handling to IOPF feature path

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Thursday, March 16, 2023 4:17 PM
> 
> On 2023/3/16 15:17, Tian, Kevin wrote:
> >> From: Lu Baolu <baolu.lu@...ux.intel.com>
> >> Sent: Thursday, March 9, 2023 10:57 AM
> >>
> >> @@ -4689,17 +4704,21 @@ static int intel_iommu_disable_iopf(struct
> device
> >> *dev)
> >>   {
> >>   	struct device_domain_info *info = dev_iommu_priv_get(dev);
> >>   	struct intel_iommu *iommu = info->iommu;
> >> -	int ret;
> >>
> >> -	ret = iommu_unregister_device_fault_handler(dev);
> >> -	if (ret)
> >> -		return ret;
> >> +	if (!info->pri_enabled)
> >> +		return -EINVAL;
> >>
> >> -	ret = iopf_queue_remove_device(iommu->iopf_queue, dev);
> >> -	if (ret)
> >> -		iommu_register_device_fault_handler(dev,
> >> iommu_queue_iopf, dev);
> >> +	pci_disable_pri(to_pci_dev(dev));
> >> +	info->pri_enabled = 0;
> >>
> >> -	return ret;
> >> +	/*
> >> +	 * With pri_enabled checked, unregistering fault handler and
> >> +	 * removing device from iopf queue should never fail.
> >> +	 */
> >> +	iommu_unregister_device_fault_handler(dev);
> >> +	iopf_queue_remove_device(iommu->iopf_queue, dev);
> >> +
> >> +	return 0;
> >>   }
> >
> > PCIe spec says that clearing the enable bit doesn't mean in-fly
> > page requests are completed:
> > --
> > Enable (E) - This field, when set, indicates that the Page Request
> > Interface is allowed to make page requests. If this field is Clear,
> > the Page Request Interface is not allowed to issue page requests.
> > If both this field and the Stopped field are Clear, then the Page
> > Request Interface will not issue new page requests, but has
> > outstanding page requests that have been transmitted or are
> > queued for transmission
> 
> Yes. So the iommu driver should drain the in-fly PRQs.
> 
> The Intel VT-d implementation drains the PRQs when any PASID is unbound
> from the iommu domain (see intel_svm_drain_prq()) before reuse. Before
> disabling iopf, the device driver should unbind pasid and disable sva,
> so when it comes here, the PRQ should have been drained.
> 
> Perhaps I can add below comments to make this clear:
> 
>          /*
>           * PCIe spec states that by clearing PRI enable bit, the Page
>           * Request Interface will not issue new page requests, but has
>           * outstanding page requests that have been transmitted or are
>           * queued for transmission. This is supposed to be called after
>           * the device driver has stopped DMA, all PASIDs have been
>           * unbound and the outstanding PRQs have been drained.
>           */
> 

this is fine. But it should be a separate patch which removes
check of return value. It's not caused by this PRI handling move
patch.