Re: [Xen-devel] [PATCH 2/3 v3] Refactor MSI restore call-chain to drop unnecessary argument

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx> 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
>
>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.
>
>-v3: Update patch description per Konrad suggestion, thanks.
>
>Tested-by: Sucheta Chakraborty <sucheta.chakraborty@xxxxxxxxxx>
>Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>

Bjorn, 
If this is not too late to add to your queue please add it with my Acked-By. 

Thanks. 

>---
> 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 87223ae..922fb49 100644
>--- a/drivers/pci/msi.c
>+++ b/drivers/pci/msi.c
>@@ -216,6 +216,8 @@ void unmask_msi_irq(struct irq_data *data)
> #ifdef HAVE_DEFAULT_MSI_RESTORE_IRQS
> void default_restore_msi_irqs(struct pci_dev *dev, int irq)
> {
>+      int pos;
>+      u16 control;
>       struct msi_desc *entry;
> 
>       entry = NULL;
>@@ -228,8 +230,19 @@ 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);
>+              }
>+      }
> }
> #endif
> 
>@@ -406,7 +419,6 @@ 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);
>@@ -430,7 +442,6 @@ 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;



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