On Sun, 27 Nov 2016 19:34:17 +0800
Cao jin <caoj.fnst@xxxxxxxxxxxxxx> wrote:
> It is user space driver's or device-specific driver's(in guest) responsbility
> to do a serious recovery when error happened. Link-reset is one part of
> recovery, when pci device is assigned to VM via vfio, link-reset will do
> twice in host & guest separately, which will cause many trouble for a
> successful recovery, so, disable the vfio-pci's link-reset in aer driver
> in host, this is a keypoint for guest to do error recovery successfully.
>
> CC: alex.williamson@xxxxxxxxxx
> CC: mst@xxxxxxxxxx
> Signed-off-by: Cao jin <caoj.fnst@xxxxxxxxxxxxxx>
> ---
> This is actually a RFC version(has debug lines left), and has minor changes in
> aer driver, so I think maybe it is better not to CC pci guys in this round.
> Later will do.
>
> drivers/pci/pcie/aer/aerdrv_core.c | 12 ++++++-
> drivers/vfio/pci/vfio_pci.c | 63 +++++++++++++++++++++++++++++++++++--
> drivers/vfio/pci/vfio_pci_private.h | 2 ++
> 3 files changed, 74 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
> index 521e39c..289fb8e 100644
> --- a/drivers/pci/pcie/aer/aerdrv_core.c
> +++ b/drivers/pci/pcie/aer/aerdrv_core.c
> @@ -496,7 +496,17 @@ static void do_recovery(struct pci_dev *dev, int severity)
> "error_detected",
> report_error_detected);
>
> - if (severity == AER_FATAL) {
> + /* vfio-pci as a general meta driver, it actually couldn't do any real
> + * recovery for device. It is user space driver, or device-specific
> + * driver in guest who should take care of the serious error recovery,
> + * link reset actually is one part of whole recovery. Doing reset_link
> + * in aer driver of host kernel for vfio-pci devices will cause many
> + * trouble for user space driver or guest's device-specific driver,
> + * for example: the serious recovery often need to read register in
> + * config space, but if register reading happens during link-resetting,
> + * it is quite possible to return invalid value like all F's, which
> + * will result in unpredictable error. */
> + if (severity == AER_FATAL && strcmp(dev->driver->name, "vfio-pci")) {
> result = reset_link(dev);
> if (result != PCI_ERS_RESULT_RECOVERED)
> goto failed;
This is not acceptable. If we want to make a path through AER recovery
that does not reset the link, there should be a way for the driver to
request it. Testing the driver name is a horrible hack. The other
question is what guarantees does vfio make that the device does get
reset? If an AER fault occurs and the user doesn't do a reset, what
happens when that device is released and a host driver tries to make
use of it? The user makes no commitment to do a reset and there are
only limited configurations where we even allow the user to perform a
reset.
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 712a849..aefd751 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -535,6 +535,15 @@ static long vfio_pci_ioctl(void *device_data,
> struct vfio_pci_device *vdev = device_data;
> unsigned long minsz;
>
> + if (vdev->aer_recovering && (cmd == VFIO_DEVICE_SET_IRQS ||
> + cmd == VFIO_DEVICE_RESET || cmd == VFIO_DEVICE_PCI_HOT_RESET)) {
> + int ret;
> + ret = wait_for_completion_interruptible(
> + &vdev->aer_error_completion);
> + if (ret)
> + return ret;
> + }
> +
> if (cmd == VFIO_DEVICE_GET_INFO) {
> struct vfio_device_info info;
>
> @@ -1117,6 +1126,7 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> vdev->irq_type = VFIO_PCI_NUM_IRQS;
> mutex_init(&vdev->igate);
> spin_lock_init(&vdev->irqlock);
> + init_completion(&vdev->aer_error_completion);
>
> ret = vfio_add_group_dev(&pdev->dev, &vfio_pci_ops, vdev);
> if (ret) {
> @@ -1176,6 +1186,9 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> {
> struct vfio_pci_device *vdev;
> struct vfio_device *device;
> + u32 uncor_status = 0;
> + unsigned int aer_cap_offset = 0;
Unnecessary initialization.
> + int ret;
>
> device = vfio_device_get_from_dev(&pdev->dev);
> if (device == NULL)
> @@ -1187,10 +1200,30 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> return PCI_ERS_RESULT_DISCONNECT;
> }
>
> + /* get device's uncorrectable error status as soon as possible,
> + * and signal it to user space. The later we read it, the possibility
> + * the register value is mangled grows. */
Bad comment style (throughout).
> + aer_cap_offset = pci_find_ext_capability(vdev->pdev, PCI_EXT_CAP_ID_ERR);
> + ret = pci_read_config_dword(vdev->pdev, aer_cap_offset +
> + PCI_ERR_UNCOR_STATUS, &uncor_status);
> + if (ret)
> + return PCI_ERS_RESULT_DISCONNECT;
> +
> + pr_err("device %d got AER detect notification. uncorrectable error status = 0x%x\n", pdev->devfn, uncor_status);//to be removed
> mutex_lock(&vdev->igate);
> +
> + vdev->aer_recovering = true;
> + reinit_completion(&vdev->aer_error_completion);
> +
> + /* suspend config space access from user space,
> + * when vfio-pci's error recovery process is on */
> + pci_cfg_access_trylock(vdev->pdev);
>
> - if (vdev->err_trigger)
> - eventfd_signal(vdev->err_trigger, 1);
> + if (vdev->err_trigger && uncor_status) {
> + pr_err("device %d signal uncor status to user space", pdev->devfn);//may be removed
> + /* signal uncorrectable error status to user space */
> + eventfd_signal(vdev->err_trigger, uncor_status);
> + }
} else... what? By bypassing the AER link reset we've assumed
responsibility for resetting the device. Even if we signal the user,
what guarantee do we have that the device is recovered?
>
> mutex_unlock(&vdev->igate);
>
> @@ -1199,8 +1232,34 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> return PCI_ERS_RESULT_CAN_RECOVER;
> }
>
> +static void vfio_pci_aer_resume(struct pci_dev *pdev)
> +{
> + struct vfio_pci_device *vdev;
> + struct vfio_device *device;
> +
> + device = vfio_device_get_from_dev(&pdev->dev);
> + if (device == NULL)
> + return;
> +
> + vdev = vfio_device_data(device);
> + if (vdev == NULL) {
> + vfio_device_put(device);
> + return;
> + }
> +
> + /* vfio-pci's error recovery is done, time to
> + * resume pci config space's accesses */
> + pci_cfg_access_unlock(vdev->pdev);
> +
> + vdev->aer_recovering = false;
> + complete_all(&vdev->aer_error_completion);
> +
> + vfio_device_put(device);
> +}
> +
> static const struct pci_error_handlers vfio_err_handlers = {
> .error_detected = vfio_pci_aer_err_detected,
> + .resume = vfio_pci_aer_resume,
> };
>
> static struct pci_driver vfio_pci_driver = {
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 8a7d546..ebf1041 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -83,6 +83,8 @@ struct vfio_pci_device {
> bool bardirty;
> bool has_vga;
> bool needs_reset;
> + bool aer_recovering;
> + struct completion aer_error_completion;
> struct pci_saved_state *pci_saved_state;
> int refcnt;
> struct eventfd_ctx *err_trigger;
--
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