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

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Message-ID: <06c9751a-417d-3c32-65af-0788593f811a@linux.intel.com>
Date:   Sat, 21 Mar 2020 09:32:45 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, 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>
Subject: Re: [PATCH 1/3] iommu/vt-d: Remove redundant IOTLB flush

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.

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]
>