[PATCH v3 6/9] spapr_pci: add spapr msi read method

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

Add spapr msi mmio read method to avoid NULL pointer dereference
issue.

Reported-by: Lei Sun <slei.casper@gmail.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/ppc/spapr_pci.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

Update v3: Add Acked-by: ...
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg08054.html

diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index 329002ac04..7033352834 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -52,6 +52,7 @@
 #include "sysemu/kvm.h"
 #include "sysemu/hostmem.h"
 #include "sysemu/numa.h"
+#include "qemu/log.h"
 
 /* Copied from the kernel arch/powerpc/platforms/pseries/msi.c */
 #define RTAS_QUERY_FN           0
@@ -738,6 +739,12 @@ static PCIINTxRoute spapr_route_intx_pin_to_irq(void *opaque, int pin)
     return route;
 }
 
+static uint64_t spapr_msi_read(void *opaque, hwaddr addr, unsigned size)
+{
+    qemu_log_mask(LOG_UNIMP, "%s not implemented\n", __func__);
+    return 0;
+}
+
 /*
  * MSI/MSIX memory region implementation.
  * The handler handles both MSI and MSIX.
@@ -755,8 +762,10 @@ static void spapr_msi_write(void *opaque, hwaddr addr,
 }
 
 static const MemoryRegionOps spapr_msi_ops = {
-    /* There is no .read as the read result is undefined by PCI spec */
-    .read = NULL,
+    /* .read result is undefined by PCI spec
+     * define .read method to avoid assert failure in memory_region_init_io
+     */
+    .read = spapr_msi_read,
     .write = spapr_msi_write,
     .endianness = DEVICE_LITTLE_ENDIAN
 };
-- 
2.26.2