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

[Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>]

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;

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.

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)

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@xxxxxxxxxx>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 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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