Re: [PATCH 2/3] PCI: Refactor MSI/MSIX mask restore code to fix interrupt lost issue

[Zhenzhong Duan <zhenzhong.duan@oracle.com>]

On 2013-10-30 05:58, Bjorn Helgaas wrote:
> On Wed, Oct 16, 2013 at 02:33:04PM +0800, Zhenzhong Duan wrote:
>> Driver init call graph under baremetal:
>> driver_init->
>>      msix_capability_init->
>>          msix_program_entries->
>>              msix_mask_irq->
>>                  entry->masked = 1
>>      request_irq->
>>          __setup_irq->
>>              irq_startup->
>>                  unmask_msi_irq->
>>                      msix_mask_irq->
>>                          entry->masked = 0;
>>
>> So entry->masked is always updated with newest value and its value could be used
>> to restore to mask register in device.
>>
>> But in initial domain (aka priviliged guest), it's different.
>> Driver init call graph under initial domain:
>> driver_init->
>>      msix_capability_init->
>>          msix_program_entries->
>>              msix_mask_irq->
>>                  entry->masked = 1
>>      request_irq->
>>          __setup_irq->
>>              irq_startup->
>>                  __startup_pirq->
>>                      EVTCHNOP_bind_pirq hypercall    (trap into Xen)
>> [Xen:]
>> pirq_guest_bind->
>>      startup_msi_irq->
>>          unmask_msi_irq->
>>              msi_set_mask_bit->
>>                  entry->msi_attrib.masked = 0;
The right mask value is saved in entry->msi_attrib.masked on Xen.
>>
>> So entry->msi_attrib.masked in xen side always has newest value. entry->masked
>> in initial domain is untouched and is 1 after msix_capability_init.
> If we run the following sequence:
>
>      pci_enable_msix()
>      request_irq()
>
> don't we end up with the MSI IRQ unmasked if we're on bare metal but masked
> if we're on Xen?  It seems like we'd want it unmasked in both cases, so I
> expected your patch to do something to make it unmasked if we're on Xen.
> But I don't think it does, does it?
>
> As far as I can tell, this patch only changes the pci_restore_state()
> path.  I think that part makes sense.
>
> Bjorn
It's unmasked on Xen too. This is just what this patch try to fix.
In PHYSDEVOP_restore_msi hypercall, xen did the right thing that did by 
kernel in baremetal.
>
>> Based on above, it's Xen's duty to restore entry->msi_attrib.masked to device,
>> but with current code, entry->masked is used and MSI-x interrupt is masked.
>>
>> Before patch, restore call graph under initial domain:
>> pci_reset_function->
>>      pci_restore_state->
>>          __pci_restore_msix_state->
>>              arch_restore_msi_irqs->
>>                  xen_initdom_restore_msi_irqs->
>>                      PHYSDEVOP_restore_msi hypercall (first mask restore)
>>              msix_mask_irq(entry, entry->masked)     (second mask restore)
>>
>> So msix_mask_irq call in initial domain call graph needs to be removed.
>>
>> Based on this we can move the restore of the mask in default_restore_msi_irqs
>> which would avoid restoring the invalid mask under Xen. Furthermore this
>> simplifies the API by making everything related to restoring an MSI be in the
>> platform specific APIs instead of just parts of it.
>>
>> After patch, restore call graph under initial domain:
>> pci_reset_function->
>>      pci_restore_state->
>>          __pci_restore_msix_state->
>>              arch_restore_msi_irqs->
>>                  xen_initdom_restore_msi_irqs->
>>                      PHYSDEVOP_restore_msi hypercall (first mask restore)
and entry->msi_attrib.masked is restored to hardware register in 
PHYSDEVOP_restore_msi hypercall on Xen.
>>
>> Logic for baremetal is not changed.
>> Before patch, restore call graph under baremetal:
>> pci_reset_function->
>>      pci_restore_state->
>>          __pci_restore_msix_state->
>>              arch_restore_msi_irqs->
>>                  default_restore_msi_irqs->
>>              msix_mask_irq(entry, entry->masked)     (first mask restore)
>>
>> After patch, restore call graph under baremetal:
>> pci_reset_function->
>>      pci_restore_state->
>>          __pci_restore_msix_state->
>>              arch_restore_msi_irqs->
>>                  default_restore_msi_irqs->
>>                      msix_mask_irq(entry, entry->masked) (first mask restore)
>>
>> The process for MSI code is similiar.
>>
>> Tested-by: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> ---
>>   drivers/pci/msi.c |   17 ++++++++++++++---
>>   1 files changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index ecd4cdf..38237f4 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -236,6 +236,8 @@ void unmask_msi_irq(struct irq_data *data)
>>   
>>   void default_restore_msi_irqs(struct pci_dev *dev, int irq)
>>   {
>> +	int pos;
>> +	u16 control;
>>   	struct msi_desc *entry;
>>   
>>   	entry = NULL;
>> @@ -248,8 +250,19 @@ void default_restore_msi_irqs(struct pci_dev *dev, int irq)
>>   		entry = irq_get_msi_desc(irq);
>>   	}
>>   
>> -	if (entry)
>> +	if (entry) {
>>   		write_msi_msg(irq, &entry->msg);
>> +		if (dev->msix_enabled) {
>> +			msix_mask_irq(entry, entry->masked);
>> +			readl(entry->mask_base);
>> +		} else {
>> +			pos = entry->msi_attrib.pos;
>> +			pci_read_config_word(dev, pos + PCI_MSI_FLAGS,
>> +					     &control);
>> +			msi_mask_irq(entry, msi_capable_mask(control),
>> +				     entry->masked);
>> +		}
>> +	}
>>   }
>>   
>>   void __read_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
>> @@ -423,7 +436,6 @@ static void __pci_restore_msi_state(struct pci_dev *dev)
>>   	arch_restore_msi_irqs(dev, dev->irq);
>>   
>>   	pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &control);
>> -	msi_mask_irq(entry, msi_capable_mask(control), entry->masked);
>>   	control &= ~PCI_MSI_FLAGS_QSIZE;
>>   	control |= (entry->msi_attrib.multiple << 4) | PCI_MSI_FLAGS_ENABLE;
>>   	pci_write_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, control);
>> @@ -447,7 +459,6 @@ static void __pci_restore_msix_state(struct pci_dev *dev)
>>   
>>   	list_for_each_entry(entry, &dev->msi_list, list) {
>>   		arch_restore_msi_irqs(dev, entry->irq);
>> -		msix_mask_irq(entry, entry->masked);
>>   	}
>>   
>>   	control &= ~PCI_MSIX_FLAGS_MASKALL;
>> -- 
>> 1.7.3
>>