linux-kernel - Re: [PATCH v4 4/7] iommu/vt-d: Reserve RID

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Message-ID: <20230417093659.653d81e9@jacob-builder>
Date:   Mon, 17 Apr 2023 09:36:59 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org, Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 4/7] iommu/vt-d: Reserve RID_PASID from global PASID
 space

Hi Baolu,

On Mon, 10 Apr 2023 09:59:45 +0800, Baolu Lu <baolu.lu@...ux.intel.com>
wrote:

> On 4/8/23 2:05 AM, Jacob Pan wrote:
> > On VT-d platforms, RID_PASID is used for DMA request without PASID. We
> > should not treat RID_PASID special instead let it be allocated from the
> > global PASID number space. Non-zero value can be used in RID_PASID on
> > Intel VT-d.
> > 
> > For ARM, AMD and others that_always_  use 0 as RID_PASID, there is no
> > impact in that SVA PASID allocation base is 1.
> > 
> > With this change, devices do both DMA with PASID and SVA will not worry
> > about conflicts when it comes to allocating PASIDs for in-kernel DMA.
> > 
> > Signed-off-by: Jacob Pan<jacob.jun.pan@...ux.intel.com>
> > ---
> >   drivers/iommu/intel/iommu.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 9f737ef55463..cbb2670f88ca 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -3956,6 +3956,10 @@ int __init intel_iommu_init(void)
> >   
> >   	intel_iommu_enabled = 1;
> >   
> > +	/* Reserved RID_PASID from the global namespace for legacy DMA
> > */
> > +	WARN_ON(iommu_alloc_global_pasid(PASID_RID2PASID,
> > PASID_RID2PASID) !=
> > +		PASID_RID2PASID);  
> 
> How about moving above line up a bit? For example, at least before
> iommu_device_register(). This is the starting point where device drivers
> may want global PASIDs.
> 
makes sense will do.

Thanks,

Jacob