On Mon, Nov 28, 2016 at 05:32:15PM +0800, Cao jin wrote:
>
>
> On 11/28/2016 11:00 AM, Michael S. Tsirkin wrote:
> > On Sun, Nov 27, 2016 at 07:34:17PM +0800, Cao jin 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. */
> >
> > Fix multi-comment style please.
> >
> > > + if (severity == AER_FATAL && strcmp(dev->driver->name, "vfio-pci")) {
> >
> > You really want some flag in the device, or something similar.
> > Also, how do we know driver is not going away at this point?
> >
>
> I didn't think of this condition, and I don't quite follow how would driver
> go away?(device has error happened, then is removed?)
Yes - hotplug request detected. Does something prevent this?
> > > result = reset_link(dev);
> > > if (result != PCI_ERS_RESULT_RECOVERED)
> > > goto failed;
>
> > > @@ -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. */
> > > + 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 */
> >
> > what about access to memory etc? Do you need to suspend this as well?
> >
>
> Yes, this question came into my mind a little bit, but I didn't see some
> existing APIs like pci_cfg_access_xxx which can help to do this.(I am still
> not familiar with kernel)
This isn't easy to do at all.
> > > + pci_cfg_access_trylock(vdev->pdev);
> >
> > If you trylock, you need to handle failure.
>
> try lock returns 0 if access is already locked, 1 otherwise. Is it necessary
> to check its return value?
Locked by whom? You blissfully access as if it's locked by you.
>
> --
> Sincerely,
> Cao jin
>
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