[Qemu-devel] [PATCH v6 16/16] pci: remove hard-coded bar size in msix_init_exclusive_bar()

[Jason Wang <jasowang@redhat.com>]

This patch lets msix_init_exclusive_bar() can calculate the bar and
pba size based on the number of MSI-X vectors other than using a
hard-coded limit 4096. This is needed to allow device to have more
than 128 MSI_X vectors. To keep migration compatibility, keep using
4096 as bar size and 2048 for pba offset.

Notes: We don't care about the case that using vectors > 128 for
legacy machine type. Since we limit the queue max to 64, so vectors >=
65 is meaningless.

Virtio device will be the first user for this.

Cc: Keith Busch <keith.busch@intel.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/pci/msix.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/hw/pci/msix.c b/hw/pci/msix.c
index 24de260..f8748cf 100644
--- a/hw/pci/msix.c
+++ b/hw/pci/msix.c
@@ -295,29 +295,37 @@ int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
 {
     int ret;
     char *name;
+    uint32_t bar_size = 4096;
+    uint32_t bar_pba_offset = bar_size / 2;
+    uint32_t bar_pba_size = (nentries / 8 + 1) * 8;
 
     /*
      * Migration compatibility dictates that this remains a 4k
      * BAR with the vector table in the lower half and PBA in
-     * the upper half.  Do not use these elsewhere!
+     * the upper half for nentries which is lower or equal to 128.
+     * No need to care about using more than 65 entries for legacy
+     * machine types who has at most 64 queues.
      */
-#define MSIX_EXCLUSIVE_BAR_SIZE 4096
-#define MSIX_EXCLUSIVE_BAR_TABLE_OFFSET 0
-#define MSIX_EXCLUSIVE_BAR_PBA_OFFSET (MSIX_EXCLUSIVE_BAR_SIZE / 2)
-#define MSIX_EXCLUSIVE_CAP_OFFSET 0
+    if (nentries * PCI_MSIX_ENTRY_SIZE > bar_pba_offset) {
+        bar_pba_offset = nentries * PCI_MSIX_ENTRY_SIZE;
+    }
 
-    if (nentries * PCI_MSIX_ENTRY_SIZE > MSIX_EXCLUSIVE_BAR_PBA_OFFSET) {
-        return -EINVAL;
+    if (bar_pba_offset + bar_pba_size > 4096) {
+        bar_size = bar_pba_offset + bar_pba_size;
+    }
+
+    if (bar_size & (bar_size - 1)) {
+        bar_size = 1 << qemu_fls(bar_size);
     }
 
     name = g_strdup_printf("%s-msix", dev->name);
-    memory_region_init(&dev->msix_exclusive_bar, OBJECT(dev), name, MSIX_EXCLUSIVE_BAR_SIZE);
+    memory_region_init(&dev->msix_exclusive_bar, OBJECT(dev), name, bar_size);
     g_free(name);
 
     ret = msix_init(dev, nentries, &dev->msix_exclusive_bar, bar_nr,
-                    MSIX_EXCLUSIVE_BAR_TABLE_OFFSET, &dev->msix_exclusive_bar,
-                    bar_nr, MSIX_EXCLUSIVE_BAR_PBA_OFFSET,
-                    MSIX_EXCLUSIVE_CAP_OFFSET);
+                    0, &dev->msix_exclusive_bar,
+                    bar_nr, bar_pba_offset,
+                    0);
     if (ret) {
         return ret;
     }
-- 
2.1.0