msix: Add simple BAR allocation MSIX setup functions

msi_init() takes over a BAR without really specifying or allowing
specification of how it does so.  Instead, let's split it into
two interfaces, one fully specified, and one trivially easy.  This
implements the latter.  msix_init_exclusive_bar() takes over
allocating and filling a PCI BAR _exclusively_ for the use of MSIX.
When used, the matching msi_uninit_exclusive_bar() should be used
to tear it down.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/msix.c

@@ -299,6 +299,45 @@ err_config:
     return ret;
 }
 
+int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
+                            uint8_t bar_nr)
+{
+    int ret;
+    char *name;
+
+    /*
+     * 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!
+     */
+#define MSIX_EXCLUSIVE_BAR_SIZE 4096
+#define MSIX_EXCLUSIVE_BAR_PBA_OFFSET (MSIX_EXCLUSIVE_BAR_SIZE / 2)
+
+    if (nentries * PCI_MSIX_ENTRY_SIZE > MSIX_EXCLUSIVE_BAR_PBA_OFFSET) {
+        return -EINVAL;
+    }
+
+    if (asprintf(&name, "%s-msix", dev->name) == -1) {
+        return -ENOMEM;
+    }
+
+    memory_region_init(&dev->msix_exclusive_bar, name, MSIX_EXCLUSIVE_BAR_SIZE);
+
+    free(name);
+
+    ret = msix_init(dev, nentries, &dev->msix_exclusive_bar, bar_nr,
+                    MSIX_EXCLUSIVE_BAR_SIZE);
+    if (ret) {
+        memory_region_destroy(&dev->msix_exclusive_bar);
+        return ret;
+    }
+
+    pci_register_bar(dev, bar_nr, PCI_BASE_ADDRESS_SPACE_MEMORY,
+                     &dev->msix_exclusive_bar);
+
+    return 0;
+}
+
 static void msix_free_irq_entries(PCIDevice *dev)
 {
     int vector;
@@ -329,6 +368,14 @@ int msix_uninit(PCIDevice *dev, MemoryRegion *bar)
     return 0;
 }
 
+void msix_uninit_exclusive_bar(PCIDevice *dev)
+{
+    if (msix_present(dev)) {
+        msix_uninit(dev, &dev->msix_exclusive_bar);
+        memory_region_destroy(&dev->msix_exclusive_bar);
+    }
+}
+
 void msix_save(PCIDevice *dev, QEMUFile *f)
 {
     unsigned n = dev->msix_entries_nr;

hw/msix.h

@@ -7,10 +7,13 @@
 int msix_init(PCIDevice *pdev, unsigned short nentries,
               MemoryRegion *bar,
               unsigned bar_nr, unsigned bar_size);
+int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
+                            uint8_t bar_nr);
 
 void msix_write_config(PCIDevice *dev, uint32_t address, uint32_t val, int len);
 
 int msix_uninit(PCIDevice *d, MemoryRegion *bar);
+void msix_uninit_exclusive_bar(PCIDevice *dev);
 
 unsigned int msix_nr_vectors_allocated(const PCIDevice *dev);
 

hw/pci.h

@@ -222,6 +222,8 @@ struct PCIDevice {
 
     /* Space to store MSIX table */
     uint8_t *msix_table_page;
+    /* MemoryRegion container for msix exclusive BAR setup */
+    MemoryRegion msix_exclusive_bar;
     /* MMIO index used to map MSIX table and pending bit entries. */
     MemoryRegion msix_mmio;
     /* Reference-count for entries actually in use by driver. */