Messages in this thread | | | Subject | Re: [PATCH 1/3] iommu/vt-d: Add rate limited information when PRQ overflows | From | Lu Baolu <> | Date | Mon, 25 Jan 2021 16:30:41 +0800 |
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Hi Kevin,
On 2021/1/25 16:16, Tian, Kevin wrote: >> From: Lu Baolu <baolu.lu@linux.intel.com> >> Sent: Monday, January 25, 2021 2:29 PM >> >> Hi Kevin, >> >> On 2021/1/22 14:38, Tian, Kevin wrote: >>>> From: Lu Baolu <baolu.lu@linux.intel.com> >>>> Sent: Thursday, January 21, 2021 9:45 AM >>>> >>>> So that the uses could get chances to know what happened. >>>> >>>> Suggested-by: Ashok Raj <ashok.raj@intel.com> >>>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> >>>> --- >>>> drivers/iommu/intel/svm.c | 10 ++++++++-- >>>> 1 file changed, 8 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c >>>> index 033b25886e57..f49fe715477b 100644 >>>> --- a/drivers/iommu/intel/svm.c >>>> +++ b/drivers/iommu/intel/svm.c >>>> @@ -895,6 +895,7 @@ static irqreturn_t prq_event_thread(int irq, void >> *d) >>>> struct intel_iommu *iommu = d; >>>> struct intel_svm *svm = NULL; >>>> int head, tail, handled = 0; >>>> + struct page_req_dsc *req; >>>> >>>> /* Clear PPR bit before reading head/tail registers, to >>>> * ensure that we get a new interrupt if needed. */ >>>> @@ -904,7 +905,6 @@ static irqreturn_t prq_event_thread(int irq, void >> *d) >>>> head = dmar_readq(iommu->reg + DMAR_PQH_REG) & >>>> PRQ_RING_MASK; >>>> while (head != tail) { >>>> struct vm_area_struct *vma; >>>> - struct page_req_dsc *req; >>>> struct qi_desc resp; >>>> int result; >>>> vm_fault_t ret; >>>> @@ -1042,8 +1042,14 @@ 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) >>>> + if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO) { >>>> + head = dmar_readq(iommu->reg + DMAR_PQH_REG) & >>>> PRQ_RING_MASK; >>>> + req = &iommu->prq[head / sizeof(*req)]; >>>> + pr_warn_ratelimited("IOMMU: %s: Page request overflow: >>>> HEAD: %08llx %08llx", >>>> + iommu->name, ((unsigned long long >>>> *)req)[0], >>>> + ((unsigned long long *)req)[1]); >>>> writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG); >>>> + } >>>> >>> >>> Not about rate limiting but I think we may have a problem in above >>> logic. It is incorrect to always clear PRO when it's set w/o first checking >>> whether the overflow condition has been cleared. This code assumes >>> that if an overflow condition occurs it must have been cleared by earlier >>> loop when hitting this check. However since this code runs in a threaded >>> context, the overflow condition could occur even after you reset the head >>> to the tail (under some extreme condition). To be sane I think we'd better >>> read both head/tail again after seeing a pending PRO here and only clear >>> PRO when it becomes a false indicator based on latest head/tail. >>> >> >> Yes, agreed. We can check the head and tail and clear the overflow bit >> until the queue is empty. The finial code looks like: >> >> /* >> * 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) { >> 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) { >> req = &iommu->prq[head / sizeof(*req)]; >> pr_warn_ratelimited("IOMMU: %s: Page request >> overflow cleared: HEAD: %08llx %08llx", >> iommu->name, ((unsigned >> long long *)req)[0], >> ((unsigned long long >> *)req)[1]); >> writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG); >> } >> } >> >> Thought? >> > > Just a small comment. Is it useful to also print a warning in the true > overflow condition which has to wait for next interrupt to be cleared? >
That's fine. :-)
> Thanks > Kevin >
Best regards, baolu
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