linux-kernel - RE: [PATCH 3/7] iommu/vt-d: Fix PASID devTLB invalidation

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Date:   Tue, 30 Jun 2020 03:01:29 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Eric Auger" <eric.auger@...hat.com>
Subject: RE: [PATCH 3/7] iommu/vt-d: Fix PASID devTLB invalidation

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Thursday, June 25, 2020 3:26 PM
> 
> On 2020/6/23 23:43, Jacob Pan wrote:
> > DevTLB flush can be used for both DMA request with and without PASIDs.
> > The former uses PASID#0 (RID2PASID), latter uses non-zero PASID for SVA
> > usage.
> >
> > This patch adds a check for PASID value such that devTLB flush with
> > PASID is used for SVA case. This is more efficient in that multiple
> > PASIDs can be used by a single device, when tearing down a PASID entry
> > we shall flush only the devTLB specific to a PASID.
> >
> > Fixes: 6f7db75e1c46 ("iommu/vt-d: Add second level page table")

btw is it really a fix? From the description it's more like an optimization...

> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > ---
> >   drivers/iommu/intel/pasid.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> > index c81f0f17c6ba..3991a24539a1 100644
> > --- a/drivers/iommu/intel/pasid.c
> > +++ b/drivers/iommu/intel/pasid.c
> > @@ -486,7 +486,16 @@ devtlb_invalidation_with_pasid(struct
> intel_iommu *iommu,
> >   	qdep = info->ats_qdep;
> >   	pfsid = info->pfsid;
> >
> > -	qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 - VTD_PAGE_SHIFT);
> > +	/*
> > +	 * When PASID 0 is used, it indicates RID2PASID(DMA request w/o
> PASID),
> > +	 * devTLB flush w/o PASID should be used. For non-zero PASID under
> > +	 * SVA usage, device could do DMA with multiple PASIDs. It is more
> > +	 * efficient to flush devTLB specific to the PASID.
> > +	 */
> > +	if (pasid)
> 
> How about
> 
> 	if (pasid == PASID_RID2PASID)
> 		qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 -
> VTD_PAGE_SHIFT);
> 	else
> 		qi_flush_dev_iotlb_pasid(iommu, sid, pfsid, pasid, qdep, 0,
> 64 -
> VTD_PAGE_SHIFT);
> 
> ?
> 
> It makes the code more readable and still works even we reassign another
> pasid for RID2PASID.
> 
> Best regards,
> baolu
> 
> > +		qi_flush_dev_iotlb_pasid(iommu, sid, pfsid, pasid, qdep, 0,
> 64 - VTD_PAGE_SHIFT);
> > +	else
> > +		qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 -
> VTD_PAGE_SHIFT);
> >   }
> >
> >   void intel_pasid_tear_down_entry(struct intel_iommu *iommu, struct
> device *dev,
> >