[Qemu-devel] [PATCH v5 3/3] hw/pci: partially handle pci master abort

[Marcel Apfelbaum <marcel.a@redhat.com>]

A MemoryRegion with negative priority was created and
it spans over all the pci address space.
It "intercepts" the accesses to unassigned pci
address space and will follow the pci spec:
 1. returns -1 on read
 2. does nothing on write

Note: setting the RECEIVED MASTER ABORT bit in the STATUS register
      of the device that initiated the transaction will be
      implemented in another series

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
---
Changes from v4:
 - Addressed Michael S. Tsirkin comments
   - Changed PCI master_abort_mem ops endian-nes to DEVICE_LITTLE_ENDIAN
 - Fixed: overlap master_abort_mem at offset 0, not at
          bus->address_space_mem.addr

 hw/pci/pci.c             | 26 ++++++++++++++++++++++++++
 include/hw/pci/pci_bus.h |  1 +
 2 files changed, 27 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index ad1c1ca..d8a1b11 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -283,6 +283,24 @@ const char *pci_root_bus_path(PCIDevice *dev)
     return rootbus->qbus.name;
 }
 
+static uint64_t master_abort_mem_read(void *opaque, hwaddr addr, unsigned size)
+{
+   return -1ULL;
+}
+
+static void master_abort_mem_write(void *opaque, hwaddr addr, uint64_t val,
+                                   unsigned size)
+{
+}
+
+static const MemoryRegionOps master_abort_mem_ops = {
+    .read = master_abort_mem_read,
+    .write = master_abort_mem_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+};
+
+#define MASTER_ABORT_MEM_PRIORITY INT_MIN
+
 static void pci_bus_init(PCIBus *bus, DeviceState *parent,
                          const char *name,
                          MemoryRegion *address_space_mem,
@@ -294,6 +312,14 @@ static void pci_bus_init(PCIBus *bus, DeviceState *parent,
     bus->address_space_mem = address_space_mem;
     bus->address_space_io = address_space_io;
 
+
+    memory_region_init_io(&bus->master_abort_mem, OBJECT(bus),
+                          &master_abort_mem_ops, bus, "pci-master-abort",
+                          memory_region_size(bus->address_space_mem));
+    memory_region_add_subregion_overlap(bus->address_space_mem,
+                                        0, &bus->master_abort_mem,
+                                        MASTER_ABORT_MEM_PRIORITY);
+
     /* host bridge */
     QLIST_INIT(&bus->child);
 
diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
index 9df1788..2ad5edb 100644
--- a/include/hw/pci/pci_bus.h
+++ b/include/hw/pci/pci_bus.h
@@ -23,6 +23,7 @@ struct PCIBus {
     PCIDevice *parent_dev;
     MemoryRegion *address_space_mem;
     MemoryRegion *address_space_io;
+    MemoryRegion master_abort_mem;
 
     QLIST_HEAD(, PCIBus) child; /* this will be replaced by qdev later */
     QLIST_ENTRY(PCIBus) sibling;/* this will be replaced by qdev later */
-- 
1.8.3.1