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

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 8/16/2023 12:30 PM, Dexuan Cui wrote:
>> From: Kuppuswamy Sathyanarayanan
>> <sathyanarayanan.kuppuswamy@linux.intel.com>
>> 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@microsoft.com>
>>> ---
>>>
>>> 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@linux.intel.com

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