linux-kernel - Re: [PATCH v2 4/8] iommu/vt-d: Reserve RID

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Date:   Tue, 28 Mar 2023 09:29:19 -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,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org, Robin Murphy <robin.murphy@....com>,
        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 v2 4/8] iommu/vt-d: Reserve RID_PASID from global SVA
 PASID space

Hi Baolu,

On Tue, 28 Mar 2023 13:20:19 +0800, Baolu Lu <baolu.lu@...ux.intel.com>
wrote:

> On 3/28/23 7:21 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 SVA PASID number space.  
> 
> It's same to AMD and ARM SMMUv3, right? They also need an explicit
> reservation of PASID 0.
> 
yes, all IOMMU drivers need to do that. I will give it a try but might need
help to place the call.

> > 
> > Consequently, for devices also do DMA with PASID, drivers 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..61c06f7ad8f7 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;
> >   
> > +#ifdef CONFIG_INTEL_IOMMU_SVM  
> 
> Do we really need this #ifdef? IOMMU_SVA is selected by INTEL_IOMMU_SVM,
> right? So if CONFIG_INTEL_IOMMU_SVM is not set,
> iommu_sva_reserve_pasid() is just a dumb.
> 
good catch! will remove

> > +	/* Reserved RID_PASID from the global namespace for legacy DMA
> > */
> > +	iommu_sva_reserve_pasid(PASID_RID2PASID, PASID_RID2PASID);
> > +#endif
> >   	return 0;
> >   
> >   out_free_dmar:  
> 
> Best regards,
> baolu


Thanks,

Jacob