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Date: Tue, 24 Jan 2017 21:00:07 +0800
From: Cao jin <caoj.fnst@...fujitsu.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, <alex.williamson@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
<qemu-devel@...gnu.org>, <izumi.taku@...fujitsu.com>
Subject: Re: [PATCH RFC] vfio error recovery: kernel support
On 01/21/2017 01:01 AM, Michael S. Tsirkin wrote:
> On Fri, Jan 20, 2017 at 06:13:22PM +0800, Cao jin wrote:
>>
>>
>> On 01/20/2017 04:16 AM, Michael S. Tsirkin wrote:
>>> This is a design and an initial patch for kernel side for AER
>>> support in VFIO.
>>>
>>> 0. What happens now (PCIE AER only)
>>> Fatal errors cause a link reset.
>>> Non fatal errors don't.
>>> All errors stop the VM eventually, but not immediately
>>> because it's detected and reported asynchronously.
>>> Interrupts are forwarded as usual.
>>> Correctable errors are not reported to guest at all.
>>> Note: PPC EEH is different. This focuses on AER.
>>>
>>> 1. Correctable errors
>>> I don't see a need to report these to guest. So let's not.
>>>
>>> 2. Fatal errors
>>> It's not easy to handle them gracefully since link reset
>>> is needed. As a first step, let's use the existing mechanism
>>> in that case.
>>>
>>> 2. Non-fatal errors
>>> Here we could make progress by reporting them to guest
>>> and have guest handle them.
>>> Issues:
>>> a. this behaviour should only be enabled with new userspace
>>> old userspace should work without changes
>>> Suggestion: One way to address this would be to add a new eventfd
>>> non_fatal_err_trigger. If not set, invoke err_trigger.
>>>
>>> b. drivers are supposed to stop MMIO when error is reported
>>> if vm keeps going, we will keep doing MMIO/config
>>> Suggestion 1: ignore this. vm stop happens much later when userspace runs anyway,
>>> so we are not making things much worse
>>> Suggestion 2: try to stop MMIO/config, resume on resume call
>>>
>>> Patch below implements Suggestion 1.
>>>
>>> c. PF driver might detect that function is completely broken,
>>> if vm keeps going, we will keep doing MMIO/config
>>> Suggestion 1: ignore this. vm stop happens much later when userspace runs anyway,
>>> so we are not making things much worse
>>> Suggestion 2: detect this and invoke err_trigger to stop VM
>>>
>>> Patch below implements Suggestion 2.
>>>
>>> Aside: we currently return PCI_ERS_RESULT_DISCONNECT when device
>>> is not attached. This seems bogus, likely based on the confusing name.
>>> We probably should return PCI_ERS_RESULT_CAN_RECOVER.
>>>
>>> The following patch does not change that.
>>>
>>> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>>>
>>> ---
>>>
>>> The patch is completely untested. Let's discuss the design first.
>>> Cao jin, if this is deemed acceptable please take it from here.
>>>
>>
>> Ok, thanks very much.
>>
>>> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
>>> index dce511f..fdca683 100644
>>> --- a/drivers/vfio/pci/vfio_pci.c
>>> +++ b/drivers/vfio/pci/vfio_pci.c
>>> @@ -1292,7 +1292,9 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>>>
>>> mutex_lock(&vdev->igate);
>>>
>>> - if (vdev->err_trigger)
>>> + if (state == pci_channel_io_normal && vdev->non_fatal_err_trigger)
>>> + eventfd_signal(vdev->err_trigger, 1);
>>> + else if (vdev->err_trigger)
>>> eventfd_signal(vdev->err_trigger, 1);
>>>
>>> mutex_unlock(&vdev->igate);
>>> @@ -1302,8 +1304,38 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
>>> return PCI_ERS_RESULT_CAN_RECOVER;
>>> }
>>>
>>> +static pci_ers_result_t vfio_pci_aer_slot_reset(struct pci_dev *pdev,
>>> + pci_channel_state_t state)
>>> +{
>>> + struct vfio_pci_device *vdev;
>>> + struct vfio_device *device;
>>> +
>>> + device = vfio_device_get_from_dev(&pdev->dev);
>>> + if (!device)
>>> + goto err_dev;
>>> +
>>> + vdev = vfio_device_data(device);
>>> + if (!vdev)
>>> + goto err_dev;
>>> +
>>> + mutex_lock(&vdev->igate);
>>> +
>>> + if (vdev->err_trigger)
>>> + eventfd_signal(vdev->err_trigger, 1);
>>> +
>>> + mutex_unlock(&vdev->igate);
>>> +
>>> + vfio_device_put(device);
>>> +
>>> +err_data:
>>> + vfio_device_put(device);
>>> +err_dev:
>>> + return PCI_ERS_RESULT_RECOVERED;
>>> +}
>>> +
>>> static const struct pci_error_handlers vfio_err_handlers = {
>>> .error_detected = vfio_pci_aer_err_detected,
>>> + .slot_reset = vfio_pci_aer_slot_reset,
>>> };
>>>
>>
>> if .slot_reset wants to be called, .error_detected should return
>> PCI_ERS_RESULT_NEED_RESET, as pci-error-recovery.txt said, so does code.
>>
>> Is .slot_reset now just a copy of .error_detected and we are going do
>> some tricks here? or else don't get why .slot_reset signal user again.
>
>
> No. We do not want a slot reset. But it might be triggered by
> another (PF) driver on the slot. If that happens some driver did something
> to make devices in the slot go to reset and our driver must recover.
> We can't recover however, so let's stop the VM.
>
> Basically the design is simple
> - if you can keep going - do
> - if you can't - ask qemu to stop guest
>
> Don't worry about adding more conditions to trigger reset etc
> at this point. Do that with later patches on-top.
>
It take me for a long while to find what I missed. I missed much
details in pci-error-recovery.txt, and I was not conscious of a
multi-function device which could have different functions(driver) on it.
Thank you both.
--
Sincerely,
Cao jin
>>> static struct pci_driver vfio_pci_driver = {
>>> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
>>> index 1c46045..e883db5 100644
>>> --- a/drivers/vfio/pci/vfio_pci_intrs.c
>>> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
>>> @@ -611,6 +611,17 @@ static int vfio_pci_set_err_trigger(struct vfio_pci_device *vdev,
>>> count, flags, data);
>>> }
>>>
>>> +static int vfio_pci_set_non_fatal_err_trigger(struct vfio_pci_device *vdev,
>>> + unsigned index, unsigned start,
>>> + unsigned count, uint32_t flags, void *data)
>>> +{
>>> + if (index != VFIO_PCI_NON_FATAL_ERR_IRQ_INDEX || start != 0 || count > 1)
>>> + return -EINVAL;
>>> +
>>> + return vfio_pci_set_ctx_trigger_single(&vdev->non_fatal_err_trigger,
>>> + count, flags, data);
>>> +}
>>> +
>>> static int vfio_pci_set_req_trigger(struct vfio_pci_device *vdev,
>>> unsigned index, unsigned start,
>>> unsigned count, uint32_t flags, void *data)
>>> @@ -664,6 +675,14 @@ int vfio_pci_set_irqs_ioctl(struct vfio_pci_device *vdev, uint32_t flags,
>>> break;
>>> }
>>> break;
>>> + case VFIO_PCI_NON_FATAL_ERR_IRQ_INDEX:
>>> + switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
>>> + case VFIO_IRQ_SET_ACTION_TRIGGER:
>>> + if (pci_is_pcie(vdev->pdev))
>>> + func = vfio_pci_set_err_trigger;
>>
>> s/vfio_pci_set_err_trigger/vfio_pci_set_non_fatal_err_trigger
>
> Right.
>
>>> + break;
>>> + }
>>> + break;
>>> case VFIO_PCI_REQ_IRQ_INDEX:
>>> switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
>>> case VFIO_IRQ_SET_ACTION_TRIGGER:
>>> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
>>> index f37c73b..c27a507 100644
>>> --- a/drivers/vfio/pci/vfio_pci_private.h
>>> +++ b/drivers/vfio/pci/vfio_pci_private.h
>>> @@ -93,6 +93,7 @@ struct vfio_pci_device {
>>> struct pci_saved_state *pci_saved_state;
>>> int refcnt;
>>> struct eventfd_ctx *err_trigger;
>>> + struct eventfd_ctx *non_fatal_err_trigger;
>>> struct eventfd_ctx *req_trigger;
>>> struct list_head dummy_resources_list;
>>> };
>>>
>>
>> --
>> Sincerely,
>> Cao jin
>>
>
>
> .
>
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