[PATCH v3] xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
the table is filled. Then it disables INTx just before clearing MASKALL
bit. Currently this approach is rejected by xen-pciback.
According to the PCIe spec, device cannot use INTx when MSI/MSI-X is
enabled (in other words: enabling MSI/MSI-X implicitly disables INTx).

Change the logic to consider INTx disabled if MSI/MSI-X is enabled. This
applies to three places:
 - checking currently enabled interrupts type,
 - transition to MSI/MSI-X - where INTx would be implicitly disabled,
 - clearing INTx disable bit - which can be allowed even if MSI/MSI-X is
   enabled, as device should consider INTx disabled anyway in that case

Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
Changes in v3:
 - allow clearing INTx regardless of MSI/MSI-X state, to be consistent
   with enabling MSI/MSI-X
Changes in v2:
 - restructure the patch to consider not only MASKALL bit, but enabling
   MSI/MSI-X generally, without explicitly disabling INTx first
---
 drivers/xen/xen-pciback/conf_space.c          | 19 +++++++++++------
 .../xen/xen-pciback/conf_space_capability.c   |  3 ++-
 drivers/xen/xen-pciback/conf_space_header.c   | 21 +++----------------
 3 files changed, 18 insertions(+), 25 deletions(-)

diff --git a/drivers/xen/xen-pciback/conf_space.c 
b/drivers/xen/xen-pciback/conf_space.c
index 059de92aea7d..d47eee6c5143 100644
--- a/drivers/xen/xen-pciback/conf_space.c
+++ b/drivers/xen/xen-pciback/conf_space.c
@@ -288,12 +288,6 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
        u16 val;
        int ret = 0;
 
-       err = pci_read_config_word(dev, PCI_COMMAND, &val);
-       if (err)
-               return err;
-       if (!(val & PCI_COMMAND_INTX_DISABLE))
-               ret |= INTERRUPT_TYPE_INTX;
-
        /*
         * Do not trust dev->msi(x)_enabled here, as enabling could be done
         * bypassing the pci_*msi* functions, by the qemu.
@@ -316,6 +310,19 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
                if (val & PCI_MSIX_FLAGS_ENABLE)
                        ret |= INTERRUPT_TYPE_MSIX;
        }
+
+       /*
+        * PCIe spec says device cannot use INTx if MSI/MSI-X is enabled,
+        * so check for INTx only when both are disabled.
+        */
+       if (!ret) {
+               err = pci_read_config_word(dev, PCI_COMMAND, &val);
+               if (err)
+                       return err;
+               if (!(val & PCI_COMMAND_INTX_DISABLE))
+                       ret |= INTERRUPT_TYPE_INTX;
+       }
+
        return ret ?: INTERRUPT_TYPE_NONE;
 }
 
diff --git a/drivers/xen/xen-pciback/conf_space_capability.c 
b/drivers/xen/xen-pciback/conf_space_capability.c
index 097316a74126..eb4c1af44f5c 100644
--- a/drivers/xen/xen-pciback/conf_space_capability.c
+++ b/drivers/xen/xen-pciback/conf_space_capability.c
@@ -236,10 +236,11 @@ static int msi_msix_flags_write(struct pci_dev *dev, int 
offset, u16 new_value,
                return PCIBIOS_SET_FAILED;
 
        if (new_value & field_config->enable_bit) {
-               /* don't allow enabling together with other interrupt types */
+               /* don't allow enabling together with other interrupt type */
                int int_type = xen_pcibk_get_interrupt_type(dev);
 
                if (int_type == INTERRUPT_TYPE_NONE ||
+                   int_type == INTERRUPT_TYPE_INTX ||
                    int_type == field_config->int_type)
                        goto write;
                return PCIBIOS_SET_FAILED;
diff --git a/drivers/xen/xen-pciback/conf_space_header.c 
b/drivers/xen/xen-pciback/conf_space_header.c
index 981435103af1..fc0332645966 100644
--- a/drivers/xen/xen-pciback/conf_space_header.c
+++ b/drivers/xen/xen-pciback/conf_space_header.c
@@ -104,24 +104,9 @@ static int command_write(struct pci_dev *dev, int offset, 
u16 value, void *data)
                pci_clear_mwi(dev);
        }
 
-       if (dev_data && dev_data->allow_interrupt_control) {
-               if ((cmd->val ^ value) & PCI_COMMAND_INTX_DISABLE) {
-                       if (value & PCI_COMMAND_INTX_DISABLE) {
-                               pci_intx(dev, 0);
-                       } else {
-                               /* Do not allow enabling INTx together with MSI 
or MSI-X. */
-                               switch (xen_pcibk_get_interrupt_type(dev)) {
-                               case INTERRUPT_TYPE_NONE:
-                                       pci_intx(dev, 1);
-                                       break;
-                               case INTERRUPT_TYPE_INTX:
-                                       break;
-                               default:
-                                       return PCIBIOS_SET_FAILED;
-                               }
-                       }
-               }
-       }
+       if (dev_data && dev_data->allow_interrupt_control &&
+           ((cmd->val ^ value) & PCI_COMMAND_INTX_DISABLE))
+               pci_intx(dev, !(value & PCI_COMMAND_INTX_DISABLE));
 
        cmd->val = value;
 
-- 
2.37.3