linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Make intel_iommu_drain_pasid

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Message-ID: <a58b8c10-2d7d-4b26-9e9b-fa0f1cb90d2e@linux.intel.com>
Date: Mon, 20 Jan 2025 17:54:49 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 "Liu, Yi L" <yi.l.liu@...el.com>
Cc: baolu.lu@...ux.intel.com, "iommu@...ts.linux.dev"
 <iommu@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d: Make intel_iommu_drain_pasid_prq() cover
 faults for RID

On 2025/1/20 17:26, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Monday, January 20, 2025 4:02 PM
>>
>> This driver supports page faults on PCI RID since commit <9f831c16c69e>
>> ("iommu/vt-d: Remove the pasid present check in prq_event_thread") by
>> allowing the reporting of page faults with the pasid_present field cleared
>> to the upper layer for further handling. The fundamental assumption here
>> is that the detach or replace operations act as a fence for page faults.
>> This implies that all pending page faults associated with a specific RID
>> or PASID are flushed when a domain is detached or replaced from a device
>> RID or PASID.
>>
>> However, the intel_iommu_drain_pasid_prq() helper does not correctly
>> handle faults for RID. This leads to faults potentially remaining pending
>> in the iommu hardware queue even after the domain is detached, thereby
>> violating the aforementioned assumption.
>>
>> Fix this issue by extending intel_iommu_drain_pasid_prq() to cover faults
>> for RID.
>>
>> Fixes: 9f831c16c69e ("iommu/vt-d: Remove the pasid present check in
>> prq_event_thread")
>> Cc: stable@...r.kernel.org
>> Suggested-by: Kevin Tian <kevin.tian@...el.com>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/intel/prq.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/intel/prq.c b/drivers/iommu/intel/prq.c
>> index c2d792db52c3..043f02d7b460 100644
>> --- a/drivers/iommu/intel/prq.c
>> +++ b/drivers/iommu/intel/prq.c
>> @@ -87,7 +87,8 @@ void intel_iommu_drain_pasid_prq(struct device *dev,
>> u32 pasid)
>>   		struct page_req_dsc *req;
>>
>>   		req = &iommu->prq[head / sizeof(*req)];
>> -		if (!req->pasid_present || req->pasid != pasid) {
>> +		if (req->rid != sid ||
>> +		    (req->pasid_present && req->pasid != pasid)) {
>>   			head = (head + sizeof(*req)) & PRQ_RING_MASK;
>>   			continue;
>>   		}
> 
> Ah you'd also want to skip (!req->pasid_present &&
> pasid != IOMMU_NO_PASID)
> 

Yes. Will make it like this,

diff --git a/drivers/iommu/intel/prq.c b/drivers/iommu/intel/prq.c
index c2d792db52c3..064194399b38 100644
--- a/drivers/iommu/intel/prq.c
+++ b/drivers/iommu/intel/prq.c
@@ -87,7 +87,9 @@ void intel_iommu_drain_pasid_prq(struct device *dev, 
u32 pasid)
                 struct page_req_dsc *req;

                 req = &iommu->prq[head / sizeof(*req)];
-               if (!req->pasid_present || req->pasid != pasid) {
+               if (req->rid != sid ||
+                   (req->pasid_present && pasid != req->pasid) ||
+                   (!req->pasid_present && pasid != IOMMU_NO_PASID)) {
                         head = (head + sizeof(*req)) & PRQ_RING_MASK;
                         continue;
                 }

Thanks,
baolu