[PATCH v10 15/17] xen/arm: account IO handlers for emulated PCI MSI-X

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

At the moment, we always allocate an extra 16 slots for IO handlers
(see MAX_IO_HANDLER). So while adding IO trap handlers for the emulated
MSI-X registers we need to explicitly tell that we have additional IO
handlers, so those are accounted.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
Cc: Julien Grall <julien@xxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
This actually moved here from the part 2 of the prep work for PCI
passthrough on Arm as it seems to be the proper place for it.

Since v5:
- optimize with IS_ENABLED(CONFIG_HAS_PCI_MSI) since VPCI_MAX_VIRT_DEV is
  defined unconditionally
New in v5
---
 xen/arch/arm/vpci.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/vpci.c b/xen/arch/arm/vpci.c
index 58e2a20135..01b50d435e 100644
--- a/xen/arch/arm/vpci.c
+++ b/xen/arch/arm/vpci.c
@@ -134,6 +134,8 @@ static int vpci_get_num_handlers_cb(struct domain *d,
 
 unsigned int domain_vpci_get_num_mmio_handlers(struct domain *d)
 {
+    unsigned int count;
+
     if ( !has_vpci(d) )
         return 0;
 
@@ -154,7 +156,17 @@ unsigned int domain_vpci_get_num_mmio_handlers(struct 
domain *d)
      * For guests each host bridge requires one region to cover the
      * configuration space. At the moment, we only expose a single host bridge.
      */
-    return 1;
+    count = 1;
+
+    /*
+     * There's a single MSI-X MMIO handler that deals with both PBA
+     * and MSI-X tables per each PCI device being passed through.
+     * Maximum number of emulated virtual devices is VPCI_MAX_VIRT_DEV.
+     */
+    if ( IS_ENABLED(CONFIG_HAS_PCI_MSI) )
+        count += VPCI_MAX_VIRT_DEV;
+
+    return count;
 }
 
 /*
-- 
2.42.0