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From: Lu Baolu <baolu.lu@linux.intel.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
	Rafael Wysocki <rafael.j.wysocki@intel.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Raj Ashok <ashok.raj@intel.com>,
	Jean Delvare <khali@linux-fr.org>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v5 15/23] iommu: handle page response timeout
Date: Wed, 30 May 2018 15:46:00 +0800	[thread overview]
Message-ID: <5B0E56B8.3010606@linux.intel.com> (raw)
In-Reply-To: <20180529092058.1942b223@jacob-builder>

Hi,

On 05/30/2018 12:20 AM, Jacob Pan wrote:
> On Mon, 14 May 2018 15:43:54 +0800
> Lu Baolu <baolu.lu@linux.intel.com> wrote:
>
>> Hi,
>>
>> On 05/12/2018 04:54 AM, Jacob Pan wrote:
>>> When IO page faults are reported outside IOMMU subsystem, the page
>>> request handler may fail for various reasons. E.g. a guest received
>>> page requests but did not have a chance to run for a long time. The
>>> irresponsive behavior could hold off limited resources on the
>>> pending device.
>>> There can be hardware or credit based software solutions as
>>> suggested in the PCI ATS Ch-4. To provide a basic safty net this
>>> patch introduces a per device deferrable timer which monitors the
>>> longest pending page fault that requires a response. Proper action
>>> such as sending failure response code could be taken when timer
>>> expires but not included in this patch. We need to consider the
>>> life cycle of page groupd ID to prevent confusion with reused group
>>> ID by a device. For now, a warning message provides clue of such
>>> failure.
>>>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
>>> ---
>>>  drivers/iommu/iommu.c | 53
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>>> include/linux/iommu.h |  4 ++++ 2 files changed, 57 insertions(+)
>>>
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index 02fed3e..1f2f49e 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -827,6 +827,37 @@ int iommu_group_unregister_notifier(struct
>>> iommu_group *group, }
>>>  EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
>>>  
>>> +static void iommu_dev_fault_timer_fn(struct timer_list *t)
>>> +{
>>> +	struct iommu_fault_param *fparam = from_timer(fparam, t,
>>> timer);
>>> +	struct iommu_fault_event *evt;
>>> +
>>> +	u64 now;
>>> +
>>> +	now = get_jiffies_64();
>>> +
>>> +	/* The goal is to ensure driver or guest page fault
>>> handler(via vfio)
>>> +	 * send page response on time. Otherwise, limited queue
>>> resources
>>> +	 * may be occupied by some irresponsive guests or drivers.
>>> +	 * When per device pending fault list is not empty, we
>>> periodically checks
>>> +	 * if any anticipated page response time has expired.
>>> +	 *
>>> +	 * TODO:
>>> +	 * We could do the following if response time expires:
>>> +	 * 1. send page response code FAILURE to all pending PRQ
>>> +	 * 2. inform device driver or vfio
>>> +	 * 3. drain in-flight page requests and responses for this
>>> device
>>> +	 * 4. clear pending fault list such that driver can
>>> unregister fault
>>> +	 *    handler(otherwise blocked when pending faults are
>>> present).
>>> +	 */
>>> +	list_for_each_entry(evt, &fparam->faults, list) {
>>> +		if (time_after64(now, evt->expire))
>>> +			pr_err("Page response time expired!, pasid
>>> %d gid %d exp %llu now %llu\n",
>>> +				evt->pasid,
>>> evt->page_req_group_id, evt->expire, now);
>>> +	}
>>> +	mod_timer(t, now + prq_timeout);
>>> +}
>>> +  
>> This timer scheme is very rough.
>>
> yes, the timer is a rough safety net for misbehaved PRQ handlers such
> as a guest.
>> The timer expires every 10 seconds (by default).
>>
>> 0                   10                 20
>> 30                 40
>> +---------------+---------------+---------------+---------------+ ^
>> ^   ^  ^                        ^ |   |     |
>> |                         | F0 F1  F2 F3
>> (F1,F2,F3 will not be handled until here!)
>>
>> F0, F1, F2, F3 are four page faults happens during [0, 10s) time
>> window. F1, F2, F3 timeout won't be handled until the timer expires
>> again at 20s. That means a fault might be pending there until about
>> (2 * prq_timeout) seconds later.
>>
> correct. it could be 2x for the worst case. I should explain in
> comments.
>> Out of curiosity, Why not adding a timer in iommu_fault_event,
>> starting it in iommu_report_device_fault() and removing it in
>> iommu_page_response()?
>>
> I thought about that also but since we are just trying to have a broad
> and rough safety net (in addition to potential HW mechanism or credit
> based solution), my thought was that having a per device timer is more
> economical than per event.
> Thanks for the in-depth check!

Okay,  got your idea. Thanks for explanation.

Best regards,
Lu Baolu

  reply	other threads:[~2018-05-30  7:46 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-11 20:53 [PATCH v5 00/23] IOMMU and VT-d driver support for Shared Virtual Address (SVA) Jacob Pan
2018-05-11 20:53 ` [PATCH v5 01/23] iommu: introduce bind_pasid_table API function Jacob Pan
2018-08-23 16:34   ` Auger Eric
2018-08-24 12:47     ` Liu, Yi L
2018-08-24 13:20       ` Auger Eric
2018-08-28 17:04         ` Jacob Pan
2018-08-24 15:00   ` Auger Eric
2018-08-28  5:14     ` Jacob Pan
2018-08-28  8:34       ` Auger Eric
2018-08-28 16:36         ` Jacob Pan
2018-05-11 20:53 ` [PATCH v5 02/23] iommu/vt-d: move device_domain_info to header Jacob Pan
2018-05-11 20:53 ` [PATCH v5 03/23] iommu/vt-d: add a flag for pasid table bound status Jacob Pan
2018-05-13  7:33   ` Lu Baolu
2018-05-14 18:51     ` Jacob Pan
2018-05-13  8:01   ` Lu Baolu
2018-05-14 18:52     ` Jacob Pan
2018-05-11 20:53 ` [PATCH v5 04/23] iommu/vt-d: add bind_pasid_table function Jacob Pan
2018-05-13  9:29   ` Lu Baolu
2018-05-14 20:22     ` Jacob Pan
2018-05-11 20:53 ` [PATCH v5 05/23] iommu: introduce iommu invalidate API function Jacob Pan
2018-05-11 20:53 ` [PATCH v5 06/23] iommu/vt-d: add definitions for PFSID Jacob Pan
2018-05-14  1:36   ` Lu Baolu
2018-05-14 20:30     ` Jacob Pan
2018-05-11 20:53 ` [PATCH v5 07/23] iommu/vt-d: fix dev iotlb pfsid use Jacob Pan
2018-05-14  1:52   ` Lu Baolu
2018-05-14 20:38     ` Jacob Pan
2018-05-11 20:54 ` [PATCH v5 08/23] iommu/vt-d: support flushing more translation cache types Jacob Pan
2018-05-14  2:18   ` Lu Baolu
2018-05-14 20:46     ` Jacob Pan
2018-05-17  8:44   ` kbuild test robot
2018-05-11 20:54 ` [PATCH v5 09/23] iommu/vt-d: add svm/sva invalidate function Jacob Pan
2018-05-14  3:35   ` Lu Baolu
2018-05-14 20:49     ` Jacob Pan
2018-05-11 20:54 ` [PATCH v5 10/23] iommu: introduce device fault data Jacob Pan
2018-09-21 10:07   ` Auger Eric
2018-09-21 17:05     ` Jacob Pan
2018-09-26 10:20       ` Auger Eric
2018-05-11 20:54 ` [PATCH v5 11/23] driver core: add per device iommu param Jacob Pan
2018-05-14  5:27   ` Lu Baolu
2018-05-14 20:52     ` Jacob Pan
2018-05-11 20:54 ` [PATCH v5 12/23] iommu: add a timeout parameter for prq response Jacob Pan
2018-05-11 20:54 ` [PATCH v5 13/23] iommu: introduce device fault report API Jacob Pan
2018-05-14  6:01   ` Lu Baolu
2018-05-14 20:55     ` Jacob Pan
2018-05-15  6:52       ` Lu Baolu
2018-05-17 11:41   ` Liu, Yi L
2018-05-17 15:59     ` Jacob Pan
2018-05-17 23:22       ` Liu, Yi L
2018-05-21 23:03         ` Jacob Pan
2018-09-06  9:25   ` Auger Eric
2018-09-06 12:42     ` Jean-Philippe Brucker
2018-09-06 13:14       ` Auger Eric
2018-09-06 17:06         ` Jean-Philippe Brucker
2018-09-07  7:11           ` Auger Eric
2018-09-07 11:23             ` Jean-Philippe Brucker
2018-09-14 13:24   ` Auger Eric
2018-09-17 16:57     ` Jacob Pan
2018-09-25 14:58   ` Jean-Philippe Brucker
2018-09-25 22:17     ` Jacob Pan
2018-09-26 10:14       ` Jean-Philippe Brucker
2018-05-11 20:54 ` [PATCH v5 14/23] iommu: introduce page response function Jacob Pan
2018-05-14  6:39   ` Lu Baolu
2018-05-29 16:13     ` Jacob Pan
2018-09-10 14:52   ` Auger Eric
2018-09-10 17:50     ` Jacob Pan
2018-09-10 19:06       ` Auger Eric
2018-05-11 20:54 ` [PATCH v5 15/23] iommu: handle page response timeout Jacob Pan
2018-05-14  7:43   ` Lu Baolu
2018-05-29 16:20     ` Jacob Pan
2018-05-30  7:46       ` Lu Baolu [this message]
2018-05-11 20:54 ` [PATCH v5 16/23] iommu/config: add build dependency for dmar Jacob Pan
2018-05-11 20:54 ` [PATCH v5 17/23] iommu/vt-d: report non-recoverable faults to device Jacob Pan
2018-05-14  8:17   ` Lu Baolu
2018-05-29 17:33     ` Jacob Pan
2018-05-11 20:54 ` [PATCH v5 18/23] iommu/intel-svm: report device page request Jacob Pan
2018-05-11 20:54 ` [PATCH v5 19/23] iommu/intel-svm: replace dev ops with fault report API Jacob Pan
2018-05-11 20:54 ` [PATCH v5 20/23] iommu/intel-svm: do not flush iotlb for viommu Jacob Pan
2018-05-11 20:54 ` [PATCH v5 21/23] iommu/vt-d: add intel iommu page response function Jacob Pan
2018-05-11 20:54 ` [PATCH v5 22/23] trace/iommu: add sva trace events Jacob Pan
2018-05-11 20:54 ` [PATCH v5 23/23] iommu: use sva invalidate and device fault trace event Jacob Pan
2018-05-29 15:54 ` [PATCH v5 00/23] IOMMU and VT-d driver support for Shared Virtual Address (SVA) Jacob Pan

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