linux-kernel - Re: [PATCH 1/3] iommu/vt-d: Remove redundant IOTLB flush

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Date:   Tue, 24 Mar 2020 08:31:25 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 1/3] iommu/vt-d: Remove redundant IOTLB flush

On Sat, 21 Mar 2020 09:32:45 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> On 2020/3/21 0:20, Jacob Pan wrote:
> > On Fri, 20 Mar 2020 21:45:26 +0800
> > Lu Baolu <baolu.lu@...ux.intel.com> wrote:
> >   
> >> On 2020/3/20 12:32, Jacob Pan wrote:  
> >>> IOTLB flush already included in the PASID tear down process. There
> >>> is no need to flush again.  
> >>
> >> It seems that intel_pasid_tear_down_entry() doesn't flush the pasid
> >> based device TLB?
> >>  
> > I saw this code in intel_pasid_tear_down_entry(). Isn't the last
> > line flush the devtlb? Not in guest of course since the passdown
> > tlb flush is inclusive.
> > 
> > 	pasid_cache_invalidation_with_pasid(iommu, did, pasid);
> > 	iotlb_invalidation_with_pasid(iommu, did, pasid);
> > 
> > 	/* Device IOTLB doesn't need to be flushed in caching mode.
> > */ if (!cap_caching_mode(iommu->cap))
> > 		devtlb_invalidation_with_pasid(iommu, dev, pasid);
> >   
> 
> But devtlb_invalidation_with_pasid() doesn't do the right thing, it
> flushes the device tlb, instead of pasid-based device tlb.
> 
Hmm, you are right. But the function name is misleading, pasid argument
is not used, is there a reason why?
This is used for PASID based device IOTLB flush, right?

> static void
> devtlb_invalidation_with_pasid(struct intel_iommu *iommu,
>                                 struct device *dev, int pasid)
> {
>          struct device_domain_info *info;
>          u16 sid, qdep, pfsid;
> 
>          info = dev->archdata.iommu;
>          if (!info || !info->ats_enabled)
>                  return;
> 
>          sid = info->bus << 8 | info->devfn;
>          qdep = info->ats_qdep;
>          pfsid = info->pfsid;
> 
>          qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 - 
> VTD_PAGE_SHIFT);
> }
> 
> Best regards,
> baolu
> 
> >> Best regards,
> >> baolu
> >>  
> >>>
> >>> Cc: Lu Baolu <baolu.lu@...ux.intel.com>
> >>> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> >>> ---
> >>>    drivers/iommu/intel-svm.c | 6 ++----
> >>>    1 file changed, 2 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> >>> index 8f42d717d8d7..1483f1845762 100644
> >>> --- a/drivers/iommu/intel-svm.c
> >>> +++ b/drivers/iommu/intel-svm.c
> >>> @@ -268,10 +268,9 @@ static void intel_mm_release(struct
> >>> mmu_notifier *mn, struct mm_struct *mm)
> >>>    	 * *has* to handle gracefully without affecting other
> >>> processes. */
> >>>    	rcu_read_lock();
> >>> -	list_for_each_entry_rcu(sdev, &svm->devs, list) {
> >>> +	list_for_each_entry_rcu(sdev, &svm->devs, list)
> >>>    		intel_pasid_tear_down_entry(svm->iommu,
> >>> sdev->dev, svm->pasid);
> >>> -		intel_flush_svm_range_dev(svm, sdev, 0, -1, 0);
> >>> -	}
> >>> +
> >>>    	rcu_read_unlock();
> >>>    
> >>>    }
> >>> @@ -731,7 +730,6 @@ int intel_svm_unbind_mm(struct device *dev,
> >>> int pasid)
> >>>    			 * large and has to be physically
> >>> contiguous. So it's
> >>>    			 * hard to be as defensive as we might
> >>> like. */ intel_pasid_tear_down_entry(iommu, dev, svm->pasid);
> >>> -			intel_flush_svm_range_dev(svm, sdev, 0,
> >>> -1, 0); kfree_rcu(sdev, rcu);
> >>>    
> >>>    			if (list_empty(&svm->devs)) {
> >>>      
> > 
> > [Jacob Pan]
> >   

[Jacob Pan]