Re: [PATCH v2] PCI: hv: Fix a crash in hv_pci_restore_msi_msg() during hibernation

[Kuppuswamy Sathyanarayanan]

On 8/16/2023 12:30 PM, Dexuan Cui wrote:
> > From: Kuppuswamy Sathyanarayanan
> > <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > Sent: Wednesday, August 16, 2023 11:12 AM
> > [...]
> > On 8/16/2023 10:59 AM, Dexuan Cui wrote:
> > > When a Linux VM with an assigned PCI device runs on Hyper-V, if the PCI
> > > device driver is not loaded yet (i.e. MSI-X/MSI is not enabled on the
> > > device yet), doing a VM hibernation triggers a panic in
> > > hv_pci_restore_msi_msg() -> msi_lock_descs(&pdev->dev), because
> > > pdev->dev.msi.data is still NULL.
> > >
> > > Avoid the panic by checking if MSI-X/MSI is enabled.
> > >
> > > Fixes: dc2b453290c4 ("PCI: hv: Rework MSI handling")
> > > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> > > ---
> > >
> > > Changes in v2:
> > >       Replaced the test "if (!pdev->dev.msi.data)" with
> > > 		      "if (!pdev->msi_enabled && !pdev->msix_enabled)".
> > >         Thanks Michael!
> > >       Updated the changelog accordingly.
> > >
> > >    drivers/pci/controller/pci-hyperv.c | 3 +++
> > >    1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-
> > hyperv.c
> > > index 2d93d0c4f10d..bed3cefdaf19 100644
> > > --- a/drivers/pci/controller/pci-hyperv.c
> > > +++ b/drivers/pci/controller/pci-hyperv.c
> > > @@ -3983,6 +3983,9 @@ static int hv_pci_restore_msi_msg(struct pci_dev
> > *pdev, void *arg)
> > >    	struct msi_desc *entry;
> > >    	int ret = 0;
> > >
> > > +	if (!pdev->msi_enabled && !pdev->msix_enabled)
> > > +		return 0;
> > Isn't this is a error condition? Don't you want to return error here?
> This is not an error.  If a PCI device driver is not loaded or not installed,
> MSI-X/MSI is not enabled on the device, so pdev->msi_enabled is 0
> and pdev->msix_enabled is 0. In this case, it's still legit for a user to request
> the system (i.e. here it's a Linux VM running on Hyper-V) to hibernate -- in
> this case, we should not try to save/restore the MSI/MSI-X state, and we
> should not let the hibernation fail; here we should just ignore the device
> by returning a success ("return 0;").

Got it. Looks good to me.

Reviewed-by: sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx

> > > +
> > >    	msi_lock_descs(&pdev->dev);
> > >    	msi_for_each_desc(entry, &pdev->dev, MSI_DESC_ASSOCIATED) {
> > >    		irq_data = irq_get_irq_data(entry->irq);