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Date: Mon, 23 Mar 2015 21:52:47 +0100
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
linux-pci@...r.kernel.org, Fam Zheng <famz@...hat.com>,
Yinghai Lu <yhlu.kernel.send@...il.com>,
Ulrich Obergfell <uobergfe@...hat.com>,
Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH v2 1/4] pci: disable msi/msix at probe time
On Mon, Mar 23, 2015 at 03:45:34PM -0500, Bjorn Helgaas wrote:
> On Mon, Mar 23, 2015 at 08:22:39PM +0100, Michael S. Tsirkin wrote:
> > On Mon, Mar 23, 2015 at 01:50:06PM -0500, Bjorn Helgaas wrote:
> > > Hi Michael,
> > >
> > > On Thu, Mar 19, 2015 at 07:57:52PM +0100, Michael S. Tsirkin wrote:
> > > > commit d52877c7b1afb8c37ebe17e2005040b79cb618b0
> > > > pci/irq: let pci_device_shutdown to call pci_msi_shutdown v2
> > > >
> > > > attempted to address the problem of kexec getting
> > > > started after linux enabled msi/msix for a device,
> > > > and drivers being confused by msi being enabled,
> > > > by disabling msi at shutdown.
> > > >
> > > > But arguably, it's better to disable msi/msix when kexec
> > > > starts - for example, kexec might run after a crash (kdump)
> > > > and shutdown callbacks are not always invoked in that case.
> > > >
> > > > Cc: Yinghai Lu <yhlu.kernel.send@...il.com>
> > > > Cc: Ulrich Obergfell <uobergfe@...hat.com>
> > > > Cc: Fam Zheng <famz@...hat.com>
> > > > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > > > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > > > ---
> > > > drivers/pci/pci-driver.c | 6 ++++++
> > > > 1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > > > index 3cb2210..2ebd2a8 100644
> > > > --- a/drivers/pci/pci-driver.c
> > > > +++ b/drivers/pci/pci-driver.c
> > > > @@ -305,6 +305,12 @@ static long local_pci_probe(void *_ddi)
> > > > */
> > > > pm_runtime_get_sync(dev);
> > > > pci_dev->driver = pci_drv;
> > > > + /*
> > > > + * When using kexec, msi might be left enabled by the previous kernel,
> > > > + * this breaks things as some drivers assume msi/msi-x is off at boot.
> > > > + * Fix this by forcing msi off at startup.
> > > > + */
> > > > + pci_msi_off(pci_dev);
> > >
> > > I think this makes sense, but I have a few questions. This is a device
> > > initialization thing, so it seems like a better fit for the enumeration
> > > path, e.g,. pci_msi_init_pci_dev(), than for the driver binding path.
> > >
> > > But when CONFIG_PCI_MSI=y, pci_msi_init_pci_dev() already does basically
> > > the same thing, so we shouldn't need this change unless CONFIG_PCI_MSI is
> > > not set in the kdump kernel.
> > >
> > > If this is a problem just with kexeced kernels that don't have
> > > CONFIG_PCI_MSI=y, I think I would prefer to fix this by moving
> > > pci_msi_init_pci_dev() outside the #ifdef so it works regardless of
> > > CONFIG_PCI_MSI. That would also be nice because we could clean up the
> > > duplication between pci_msi_off() and pci_msi_init_pci_dev(). It would
> > > also make the starting machine state less dependent on the new kernel,
> > > which seems like a good thing.
> >
> > What you say above makes sense.
> > OK so the simplest fix is something like below then.
> > Fixes the duplication and kexec for CONFIG_PCI_MSI=n.
> > Acceptable? Pls let me know, if yes I'll test and
> > resubmit properly.
> >
> > > Are there any bugzillas we could reference here?
> >
> > I'll check this point. Maybe not - the real bugfix is
> > patch 2/4, this was just found by reading code,
> > but it's a dependency to make sure 2/4 does not
> > introduce regressions.
>
> OK, can you add the bugzilla link to that patch, if there is one?
>
> > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > index 0e037af..2ab59d4 100644
> > --- a/drivers/pci/msi.c
> > +++ b/drivers/pci/msi.c
> > @@ -1062,18 +1062,8 @@ EXPORT_SYMBOL(pci_msi_enabled);
> > void pci_msi_init_pci_dev(struct pci_dev *dev)
> > {
> > INIT_LIST_HEAD(&dev->msi_list);
> > -
> > - /* Disable the msi hardware to avoid screaming interrupts
> > - * during boot. This is the power on reset default so
> > - * usually this should be a noop.
> > - */
> > dev->msi_cap = pci_find_capability(dev, PCI_CAP_ID_MSI);
> > - if (dev->msi_cap)
> > - msi_set_enable(dev, 0);
> > -
> > dev->msix_cap = pci_find_capability(dev, PCI_CAP_ID_MSIX);
> > - if (dev->msix_cap)
> > - msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0);
> > }
> >
> > /**
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 8d2f400..c455501 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -1485,6 +1485,12 @@ static struct pci_dev *pci_scan_device(struct pci_bus *bus, int devfn)
> >
> > static void pci_init_capabilities(struct pci_dev *dev)
> > {
> > + /* Disable the msi hardware to avoid screaming interrupts
> > + * during boot. This is the power on reset default so
> > + * usually this should be a noop.
> > + */
> > + pci_msi_off(dev);
> > +
> > /* MSI/MSI-X list */
> > pci_msi_init_pci_dev(dev);
>
> Could we move pci_msi_init_pci_dev() from msi.c to pci.c and make it look
> something like the following?
>
> void pci_msi_off(struct pci_dev *dev)
> {
> if (dev->msi_cap) {
> ...
> }
> if (dev->msix_cap) {
> ...
> }
> }
>
> void pci_msi_init_pci_dev(struct pci_dev *dev)
> {
> #ifdef CONFIG_PCI_MSI
> INIT_LIST_HEAD(&dev->msi_list);
> #endif
>
> dev->msi_cap = pci_find_capability(dev, PCI_CAP_ID_MSI);
> dev->msix_cap = pci_find_capability(dev, PCI_CAP_ID_MSIX);
> pci_msi_off(dev);
> }
>
> Then I think we could remove pci_msi_off() calls from a couple quirks as
> well. And we'd only have one MSI-related callout from
> pci_init_capabilities().
>
> Bjorn
OK I was under the impression msi_cap/msix_cap aren't there
when CONFIG_PCI_MSI is not set, but I checked and they
actually are, so yes, will do.
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