[PATCH v2 0/2] iommu/vt-d: Some misc tweaks in SVA

[PATCH v2 0/2] iommu/vt-d: Some misc tweaks in SVA

[Lu Baolu]

This includes some misc tweaks in the VT-d SVA implementation. I will
plan them for v5.12 if no objections.

Change log:
v1->v2:
  - v1:
    https://lore.kernel.org/linux-iommu/20210121014505.1659166-1-baolu.lu@linux.intel.com/
  - Keep the logic of clearing PRO sane
  - Drop the device outstanding PRQ number patch. Need more test and
    will repost later. 

Best regards,
baolu

Lu Baolu (2):
  iommu/vt-d: Clear PRQ overflow only when PRQ is empty
  iommu/vt-d: Use INVALID response code instead of FAILURE

 drivers/iommu/intel/svm.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

-- 
2.25.1

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[PATCH v2 1/2] iommu/vt-d: Clear PRQ overflow only when PRQ is empty

[Lu Baolu]

It is incorrect to always clear PRO when it's set w/o first checking
whether the overflow condition has been cleared. Current code assumes
that if an overflow condition occurs it must have been cleared by earlier
loop. However since the code runs in a threaded context, the overflow
condition could occur even after setting the head to the tail under some
extreme condition. To be sane, we should read both head/tail again when
seeing a pending PRO and only clear PRO after all pending PRs have been
handled.

Suggested-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/linux-iommu/MWHPR11MB18862D2EA5BD432BF22D99A48CA09@MWHPR11MB1886.namprd11.prod.outlook.com/
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/svm.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 033b25886e57..d7c98c5fa4e7 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -1042,8 +1042,17 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 	 * Clear the page request overflow bit and wake up all threads that
 	 * are waiting for the completion of this handling.
 	 */
-	if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO)
-		writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG);
+	if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO) {
+		pr_info_ratelimited("IOMMU: %s: PRQ overflow detected\n",
+				    iommu->name);
+		head = dmar_readq(iommu->reg + DMAR_PQH_REG) & PRQ_RING_MASK;
+		tail = dmar_readq(iommu->reg + DMAR_PQT_REG) & PRQ_RING_MASK;
+		if (head == tail) {
+			writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG);
+			pr_info_ratelimited("IOMMU: %s: PRQ overflow cleared",
+					    iommu->name);
+		}
+	}
 
 	if (!completion_done(&iommu->prq_complete))
 		complete(&iommu->prq_complete);
-- 
2.25.1

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[PATCH v2 2/2] iommu/vt-d: Use INVALID response code instead of FAILURE

[Lu Baolu]

The VT-d IOMMU response RESPONSE_FAILURE for a page request in below
cases:

- When it gets a Page_Request with no PASID;
- When it gets a Page_Request with PASID that is not in use for this
  device.

This is allowed by the spec, but IOMMU driver doesn't support such cases
today. When the device receives RESPONSE_FAILURE, it sends the device
state machine to HALT state. Now if we try to unload the driver, it hangs
since the device doesn't send any outbound transactions to host when the
driver is trying to clear things up. The only possible responses would be
for invalidation requests.

Let's use RESPONSE_INVALID instead for now, so that the device state
machine doesn't enter HALT state.

Suggested-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/svm.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index d7c98c5fa4e7..574a7e657a9a 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -911,10 +911,8 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 		u64 address;
 
 		handled = 1;
-
 		req = &iommu->prq[head / sizeof(*req)];
-
-		result = QI_RESP_FAILURE;
+		result = QI_RESP_INVALID;
 		address = (u64)req->addr << VTD_PAGE_SHIFT;
 		if (!req->pasid_present) {
 			pr_err("%s: Page request without PASID: %08llx %08llx\n",
@@ -952,7 +950,6 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 			rcu_read_unlock();
 		}
 
-		result = QI_RESP_INVALID;
 		/* Since we're using init_mm.pgd directly, we should never take
 		 * any faults on kernel addresses. */
 		if (!svm->mm)
-- 
2.25.1

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Re: [PATCH v2 0/2] iommu/vt-d: Some misc tweaks in SVA

[Joerg Roedel]

On Tue, Jan 26, 2021 at 04:07:28PM +0800, Lu Baolu wrote:
> Lu Baolu (2):
>   iommu/vt-d: Clear PRQ overflow only when PRQ is empty
>   iommu/vt-d: Use INVALID response code instead of FAILURE
> 
>  drivers/iommu/intel/svm.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)

Applied, thanks.
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