[Qemu-devel] [PATCH] pci: Add generic PCI device option to disable 64bit MMIO BARs

[Alex Williamson <alex.williamson@redhat.com>]

As we start to enable 64bit I/O devices, there's a good chance
we'll find bugs and compatibility issues.  This allows a user
to toggle off (default on) 64bit PCI MMIO BARs, downgrading
them to 32bit BARs.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

Should this be an "x-mem64" option implying that it's really
only for debugging and may go away or could this have some
longevity?

 hw/pci.c |   18 ++++++++++++++++++
 hw/pci.h |    4 ++++
 2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/hw/pci.c b/hw/pci.c
index 57ec104..9afddb0 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -63,6 +63,8 @@ struct BusInfo pci_bus_info = {
                         QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
         DEFINE_PROP_BIT("command_serr_enable", PCIDevice, cap_present,
                         QEMU_PCI_CAP_SERR_BITNR, true),
+        DEFINE_PROP_BIT("mem64", PCIDevice, cap_present,
+                        QEMU_PCI_CAP_MEM64_BITNR, true),
         DEFINE_PROP_END_OF_LIST()
     }
 };
@@ -957,6 +959,22 @@ void pci_register_bar(PCIDevice *pci_dev, int region_num,
         exit(1);
     }
 
+    if (!(type & PCI_BASE_ADDRESS_SPACE_IO)) {
+        if (!(pci_dev->cap_present & QEMU_PCI_CAP_MEM64)) {
+            type &= ~PCI_BASE_ADDRESS_MEM_TYPE_64;
+        }
+
+        /* 32bit BARs are limited to 2GB */
+        if (size >= 0x80000000U && !(type & PCI_BASE_ADDRESS_MEM_TYPE_64)) {
+            fprintf(stderr, "Device %04x:%02x:%02x.%x BAR %d is %ld "
+                    "GB, 64bit memory type required\n",
+                    pci_find_domain(pci_dev->bus), pci_bus_num(pci_dev->bus),
+                    PCI_SLOT(pci_dev->devfn), PCI_FUNC(pci_dev->devfn),
+                    region_num, (long)(size >> 30));
+            exit(1);
+        }
+    }
+
     r = &pci_dev->io_regions[region_num];
     r->addr = PCI_BAR_UNMAPPED;
     r->size = size;
diff --git a/hw/pci.h b/hw/pci.h
index 4220151..17fd996 100644
--- a/hw/pci.h
+++ b/hw/pci.h
@@ -126,6 +126,10 @@ enum {
     /* command register SERR bit enabled */
 #define QEMU_PCI_CAP_SERR_BITNR 4
     QEMU_PCI_CAP_SERR = (1 << QEMU_PCI_CAP_SERR_BITNR),
+
+    /* expose 64bit MMIO BARs when available */
+#define QEMU_PCI_CAP_MEM64_BITNR 5
+    QEMU_PCI_CAP_MEM64 = (1 << QEMU_PCI_CAP_MEM64_BITNR),
 };
 
 typedef int (*msix_mask_notifier_func)(PCIDevice *, unsigned vector,