linux-kernel - Re: [PATCH v4 3/7] iommu: Support allocation of global PASIDs outside SVA

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Message-ID: <20230418160450.4ea7fb7d@jacob-builder>
Date:   Tue, 18 Apr 2023 16:04:50 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 3/7] iommu: Support allocation of global PASIDs
 outside SVA

Hi Baolu,

On Tue, 18 Apr 2023 10:06:12 +0800, Baolu Lu <baolu.lu@...ux.intel.com>
wrote:

> On 4/18/23 12:46 AM, Jacob Pan wrote:
> > On Wed, 12 Apr 2023 09:37:48 +0800, Baolu Lu<baolu.lu@...ux.intel.com>
> > wrote:
> >   
> >> On 4/11/23 4:02 PM, Tian, Kevin wrote:  
> >>>> From: Jacob Pan<jacob.jun.pan@...ux.intel.com>
> >>>> Sent: Saturday, April 8, 2023 2:06 AM
> >>>> @@ -28,8 +26,8 @@ static int iommu_sva_alloc_pasid(struct mm_struct
> >>>> *mm, ioasid_t min, ioasid_t ma
> >>>>    		goto out;
> >>>>    	}
> >>>>
> >>>> -	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
> >>>> GFP_KERNEL);
> >>>> -	if (ret < min)
> >>>> +	ret = iommu_alloc_global_pasid(min, max);  
> >>> I wonder whether this can take a device pointer so
> >>> dev->iommu->max_pasids is enforced inside the alloc function.  
> >> Agreed. Instead of using the open code, it looks better to have a
> >> helper like dev_iommu_max_pasids().  
> > yes, probably export dev_iommu_get_max_pasids(dev)?
> > 
> > But if I understood Kevin correctly, he's also suggesting that the
> > interface should be changed to iommu_alloc_global_pasid(dev), my
> > concern is that how do we use this function to reserve RID_PASID which
> > is not specific to a device?  
> 
> Probably we can introduce a counterpart dev->iommu->min_pasids, so that
> there's no need to reserve the RID_PASID. At present, we can set it to 1
> in the core as ARM/AMD/Intel all treat PASID 0 as a special pasid.
> 
> In the future, if VT-d supports using arbitrary number as RID_PASID for
> any specific device, we can call iommu_alloc_global_pasid() for that
> device.
> 
> The device drivers don't know and don't need to know the range of viable
> PASIDs, so the @min, @max parameters seem to be unreasonable.
Sure, that is reasonable. Another question is whether global PASID
allocation is always for a single device, if not I prefer to keep the
current iommu_alloc_global_pasid() and add a wrapper
iommu_alloc_global_pasid_dev(dev) to extract the @min, @max. OK?


Thanks,

Jacob