linux-kernel - RE: [PATCH v8 02/11] iommu: Add max_pasids field in struct dev

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Date:   Fri, 10 Jun 2022 09:01:38 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>
CC:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v8 02/11] iommu: Add max_pasids field in struct dev_iommu

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Friday, June 10, 2022 2:47 PM
> 
> On 2022/6/10 03:01, Raj, Ashok wrote:
> > On Tue, Jun 07, 2022 at 09:49:33AM +0800, Lu Baolu wrote:
> >> @@ -218,6 +219,30 @@ static void dev_iommu_free(struct device *dev)
> >>   	kfree(param);
> >>   }
> >>
> >> +static u32 dev_iommu_get_max_pasids(struct device *dev)
> >> +{
> >> +	u32 max_pasids = dev->iommu->iommu_dev->max_pasids;
> >> +	u32 num_bits;
> >> +	int ret;
> >> +
> >> +	if (!max_pasids)
> >> +		return 0;
> >> +
> >> +	if (dev_is_pci(dev)) {
> >> +		ret = pci_max_pasids(to_pci_dev(dev));
> >> +		if (ret < 0)
> >> +			return 0;
> >> +
> >> +		return min_t(u32, max_pasids, ret);
> >
> > Ah.. that answers my other question to consider device pasid-max. I guess
> > if we need any enforcement of restricting devices that aren't supporting
> > the full PASID, that will be done by some higher layer?
> 
> The mm->pasid style of SVA is explicitly enabled through
> iommu_dev_enable_feature(IOMMU_DEV_FEAT_SVA). The IOMMU driver
> specific
> restriction might be put there?
> 
> >
> > too many returns in this function, maybe setup all returns to the end of
> > the function might be elegant?
> 
> I didn't find cleanup room after a quick scan of the code. But sure, let
> me go through code again offline.
>

If we do care:

+static u32 dev_iommu_get_max_pasids(struct device *dev)
+{
+	u32 max_pasids = 0, 
+	u32 num_bits = 0;
+	int ret;
+
+	if (dev_is_pci(dev)) {
+		ret = pci_max_pasids(to_pci_dev(dev));
+		if (ret > 0)
+			max_pasids = ret;
+	} else {
+		ret = device_property_read_u32(dev, "pasid-num-bits", &num_bits);
+		if (!ret)
+			max_pasids = 1UL << num_bits;
+	}
+
+	return min_t(u32, max_pasids, dev->iommu->iommu_dev->max_pasids);
+}