From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45338) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1alo9n-0006xO-8a for qemu-devel@nongnu.org; Thu, 31 Mar 2016 21:45:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1alo9j-00024F-6n for qemu-devel@nongnu.org; Thu, 31 Mar 2016 21:45:51 -0400 Received: from [59.151.112.132] (port=37001 helo=heian.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1alo9h-000249-Sc for qemu-devel@nongnu.org; Thu, 31 Mar 2016 21:45:47 -0400 Message-ID: <56FDD17B.1090304@cn.fujitsu.com> Date: Fri, 1 Apr 2016 09:40:11 +0800 From: Chen Fan MIME-Version: 1.0 References: <1458727927-15082-1-git-send-email-caoj.fnst@cn.fujitsu.com> <1458727927-15082-12-git-send-email-caoj.fnst@cn.fujitsu.com> <20160324165428.68bbcc96@t450s.home> <56F49681.8040101@cn.fujitsu.com> <20160324202255.4a397ca8@ul30vt.home> <56FCC9CB.9060802@cn.fujitsu.com> <20160331094404.4126791b@t450s.home> In-Reply-To: <20160331094404.4126791b@t450s.home> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [patch v5 11/12] vfio: device may stuck in D3 when doing aer recovery List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex Williamson Cc: izumi.taku@jp.fujitsu.com, Cao jin , qemu-devel@nongnu.org, mst@redhat.com On 03/31/2016 11:44 PM, Alex Williamson wrote: > On Thu, 31 Mar 2016 14:55:07 +0800 > Chen Fan wrote: > >> On 03/25/2016 10:22 AM, Alex Williamson wrote: >>> On Fri, 25 Mar 2016 09:38:09 +0800 >>> Chen Fan wrote: >>> >>>> On 03/25/2016 06:54 AM, Alex Williamson wrote: >>>>> On Wed, 23 Mar 2016 18:12:06 +0800 >>>>> Cao jin wrote: >>>>> >>>>>> From: Chen Fan >>>>>> >>>>>> when a physical device aer occurred, the device state probably >>>>>> is not in D0 in a short time, if we recover the device quickly. >>>>>> we may stuck in D3 state when force to change device state to D0. >>>>>> we may need to wait for a short time to inject the error to guest. >>>>>> >>>>>> Signed-off-by: Chen Fan >>>>>> --- >>>>>> hw/vfio/pci.c | 3 +++ >>>>>> 1 file changed, 3 insertions(+) >>>>>> >>>>>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c >>>>>> index 25fc095..5216e7f 100644 >>>>>> --- a/hw/vfio/pci.c >>>>>> +++ b/hw/vfio/pci.c >>>>>> @@ -2658,6 +2658,9 @@ static void vfio_err_notifier_handler(void *opaque) >>>>>> msg.severity = isfatal ? PCI_ERR_ROOT_CMD_FATAL_EN : >>>>>> PCI_ERR_ROOT_CMD_NONFATAL_EN; >>>>>> >>>>>> + /* wait a bit to ensure aer device is ready */ >>>>>> + usleep(2 * 1000); >>>>> Where does this number come from? Why would the device be in D3? I >>>>> don't understand this at all. >>>> Hi Alex, >>>> >>>> when I tested the code in my environment, I found that when I used >>>> the aer-inject module to inject a fake aer error to device on host, the qemu >>>> would throw out the message "vfio: Unable to power on device, stuck in D3" >>>> on and off. if I use "gdb" to debug the vfio_pci_pre_reset, the phenomenon >>>> would not appearance, I just thought it should be some timing race issue, >>>> so I use a sleep() to wait 2ms (double the reset time of 1ms) to ensure the >>>> device state is ready. maybe the root reason still need to be >>>> investigated deeply. >>> Yes, it sounds like you need to investigate this further, the delay is >>> arbitrary and perhaps suggests a race that needs to be fixed >>> correctly. Thanks, >> Hi Alex, >> >> after done some investigation of the problem, I found that only >> when the injected >> error is fatal, the problem will appear. because in aer do_recovery, >> host will call reset_link >> on the root port, which would invoke pci_reset_bridge_secondary_bus in >> aer_root_reset, >> that would reset the bridge and all the device under that. so when qemu >> receive the aer >> notification, then propagate the error to guest, guest does the same way >> to perform the >> recovery, if the guest `reset_link` that will call the vfio_pre_reset >> done at the stage of host >> bridge reset, the device status would probable stick in D3. >> >> so I think after qemu receive the aer notification, we should wait for >> enough time to >> ensure the bridge has been reset completely. I just use sleep <=10ms to >> test the code, >> seems still appear the message "vfio: Unable to power on device, stuck >> in D3". so I think >> we should sleep 100ms to ensure the delay sufficient. I have tested that >> code 100+ times >> by inject aer error. the issue no longer appears. > I'm not satisfied with this. pci_reset_bridge_secondary_bus() is > invoked by both the host AER code and the guest AER code, the latter > via the vfio PCI hot reset interface. The > pci_reset_bridge_secondary_bus() function includes the spec defined > delay by which point all the devices should be operational again. The > spec also defines that devices are in D0 after reset, which implies > that the only reason we would ever be seeing a device in D3 is if we're > reading the device while it is still in reset or before it has > recovered from reset. That implies that either > pci_reset_bridge_secondary_bus() is not waiting long enough or QEMU is > allowing one device to call vfio_pre_reset while another device is > still in reset. I suspect QEMU serializes reset such that the latter > case is not possible, which means that you might have a device that > takes longer to reset than the spec defines. Such a quirk should be > handled in the host kernel reset, not by adding arbitrary delays in > userspace code. Thanks, maybe it is not the delay issue actually. let me analyze the aer process in do_recovery: host qemu guest broadcast: error_detected +--> error_detected (VFIO) +--> eventfd_signal -----> inject_aer ---------> broadcast: error_detected *reset_link* +--> error_detected (real driver) *reset_link* broadcast: mmio/slot_reset broadcast: mmio/slot_reset broadcast: resume broadcast: resume we can see that the reset_link in host and in guest are not called in order. the reset_link in guest may execute during the host broadcast "error_detected" or "reset_link" as long as there are many devices need to walk on the bus. so in the case qemu has the opportunity to call vfio_pre_reset while host is still in reset. so can we consider moving the eventfd_signal in error_detected to resume/slot_reset callback in vfio driver, then we can assure that the host reset_link finish before guest do reset_link. or adding a new resume/slot_reset event between vfio driver and qemu to delay the guest reset_link. Thanks, Chen > > Alex > > > . >