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

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
>>



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