[Qemu-devel] [PATCH RFC v3 2/2] hw/pci: handle unassigned pci addresses

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

Created a MemoryRegion with negative priority that
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
 3. sets the RECEIVED MASTER ABORT bit in the STATUS register
    of the device that initiated the transaction

Note: This implementation assumes that all the reads/writes to
the pci address space are done by the cpu.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
---
Changes from v1:
 - "pci-unassigned-mem" MemoryRegion resides now in PCIBus and not on
    various Host Bridges
 - "pci-unassgined-mem" does not have a ".valid.accept" field and
    implements read write methods

 hw/pci/pci.c             | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 include/hw/pci/pci_bus.h |  1 +
 2 files changed, 47 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index d00682e..b6a8026 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -283,6 +283,43 @@ const char *pci_root_bus_path(PCIDevice *dev)
     return rootbus->qbus.name;
 }
 
+static void unassigned_mem_access(PCIBus *bus)
+{
+    /* FIXME assumption: memory access to the pci address
+     * space is always initiated by the host bridge
+     * (device 0 on the bus) */
+    PCIDevice *d = bus->devices[0];
+    if (!d) {
+        return;
+    }
+
+    pci_word_test_and_set_mask(d->config + PCI_STATUS,
+                               PCI_STATUS_REC_MASTER_ABORT);
+}
+
+static uint64_t unassigned_mem_read(void *opaque, hwaddr addr, unsigned size)
+{
+    PCIBus *bus = opaque;
+    unassigned_mem_access(bus);
+
+    return -1ULL;
+}
+
+static void unassigned_mem_write(void *opaque, hwaddr addr, uint64_t val,
+                                unsigned size)
+{
+    PCIBus *bus = opaque;
+    unassigned_mem_access(bus);
+}
+
+static const MemoryRegionOps unassigned_mem_ops = {
+    .read = unassigned_mem_read,
+    .write = unassigned_mem_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
+#define UNASSIGNED_MEM_PRIORITY -1
+
 static void pci_bus_init(PCIBus *bus, DeviceState *parent,
                          const char *name,
                          MemoryRegion *address_space_mem,
@@ -294,6 +331,15 @@ 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->unassigned_mem, OBJECT(bus),
+                          &unassigned_mem_ops, bus, "pci-unassigned",
+                          memory_region_size(bus->address_space_mem));
+    memory_region_add_subregion_overlap(bus->address_space_mem,
+                                        bus->address_space_mem->addr,
+                                        &bus->unassigned_mem,
+                                        UNASSIGNED_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..4cc25a3 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 unassigned_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