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iommu/vt-d: Clear PRQ overflow only when PRQ is empty 

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>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/linux-iommu/MWHPR11MB18862D2EA5BD432BF22D99A48CA09@MWHPR11MB1886.namprd11.prod.outlook.com/
Link: https://lore.kernel.org/r/20210126080730.2232859-2-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Lu Baolu 2021-01-26 16:07:29 +08:00 committed by Joerg Roedel
parent a8ce9ebbec
commit 28a77185f1
1 changed files with 11 additions and 2 deletions
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13
drivers/iommu/intel/svm.c
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@ -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);