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

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Date:   Fri, 20 Mar 2020 09:20:47 -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 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);

> 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]