vfio: add region info cache

Instead of requesting region information on demand with
VFIO_DEVICE_GET_REGION_INFO, maintain a cache: this will become
necessary for performance for vfio-user, where this call becomes a
message over the control socket, so is of higher overhead than the
traditional path.

We will also need it to generalize region accesses, as that means we
can't use ->config_offset for configuration space accesses, but must
look up the region offset (if relevant) each time.

Originally-by: John Johnson <john.g.johnson@oracle.com>
Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250507152020.1254632-12-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/ccw.c

@@ -504,7 +504,6 @@ static bool vfio_ccw_get_region(VFIOCCWDevice *vcdev, Error **errp)
 
     vcdev->io_region_offset = info->offset;
     vcdev->io_region = g_malloc0(info->size);
-    g_free(info);
 
     /* check for the optional async command region */
     ret = vfio_device_get_region_info_type(vdev, VFIO_REGION_TYPE_CCW,
@@ -517,7 +516,6 @@ static bool vfio_ccw_get_region(VFIOCCWDevice *vcdev, Error **errp)
         }
         vcdev->async_cmd_region_offset = info->offset;
         vcdev->async_cmd_region = g_malloc0(info->size);
-        g_free(info);
     }
 
     ret = vfio_device_get_region_info_type(vdev, VFIO_REGION_TYPE_CCW,
@@ -530,7 +528,6 @@ static bool vfio_ccw_get_region(VFIOCCWDevice *vcdev, Error **errp)
         }
         vcdev->schib_region_offset = info->offset;
         vcdev->schib_region = g_malloc(info->size);
-        g_free(info);
     }
 
     ret = vfio_device_get_region_info_type(vdev, VFIO_REGION_TYPE_CCW,
@@ -544,7 +541,6 @@ static bool vfio_ccw_get_region(VFIOCCWDevice *vcdev, Error **errp)
         }
         vcdev->crw_region_offset = info->offset;
         vcdev->crw_region = g_malloc(info->size);
-        g_free(info);
     }
 
     return true;
@@ -554,7 +550,6 @@ out_err:
     g_free(vcdev->schib_region);
     g_free(vcdev->async_cmd_region);
     g_free(vcdev->io_region);
-    g_free(info);
     return false;
 }
 

hw/vfio/device.c

@@ -202,6 +202,12 @@ int vfio_device_get_region_info(VFIODevice *vbasedev, int index,
     size_t argsz = sizeof(struct vfio_region_info);
     int ret;
 
+    /* check cache */
+    if (vbasedev->reginfo[index] != NULL) {
+        *info = vbasedev->reginfo[index];
+        return 0;
+    }
+
     *info = g_malloc0(argsz);
 
     (*info)->index = index;
@@ -222,6 +228,9 @@ retry:
         goto retry;
     }
 
+    /* fill cache */
+    vbasedev->reginfo[index] = *info;
+
     return 0;
 }
 
@@ -240,7 +249,6 @@ int vfio_device_get_region_info_type(VFIODevice *vbasedev, uint32_t type,
 
         hdr = vfio_get_region_info_cap(*info, VFIO_REGION_INFO_CAP_TYPE);
         if (!hdr) {
-            g_free(*info);
             continue;
         }
 
@@ -252,8 +260,6 @@ int vfio_device_get_region_info_type(VFIODevice *vbasedev, uint32_t type,
         if (cap_type->type == type && cap_type->subtype == subtype) {
             return 0;
         }
-
-        g_free(*info);
     }
 
     *info = NULL;
@@ -262,7 +268,7 @@ int vfio_device_get_region_info_type(VFIODevice *vbasedev, uint32_t type,
 
 bool vfio_device_has_region_cap(VFIODevice *vbasedev, int region, uint16_t cap_type)
 {
-    g_autofree struct vfio_region_info *info = NULL;
+    struct vfio_region_info *info = NULL;
     bool ret = false;
 
     if (!vfio_device_get_region_info(vbasedev, region, &info)) {
@@ -435,10 +441,21 @@ void vfio_device_prepare(VFIODevice *vbasedev, VFIOContainerBase *bcontainer,
     QLIST_INSERT_HEAD(&bcontainer->device_list, vbasedev, container_next);
 
     QLIST_INSERT_HEAD(&vfio_device_list, vbasedev, global_next);
+
+    vbasedev->reginfo = g_new0(struct vfio_region_info *,
+                               vbasedev->num_regions);
 }
 
 void vfio_device_unprepare(VFIODevice *vbasedev)
 {
+    int i;
+
+    for (i = 0; i < vbasedev->num_regions; i++) {
+        g_free(vbasedev->reginfo[i]);
+    }
+    g_free(vbasedev->reginfo);
+    vbasedev->reginfo = NULL;
+
     QLIST_REMOVE(vbasedev, container_next);
     QLIST_REMOVE(vbasedev, global_next);
     vbasedev->bcontainer = NULL;

hw/vfio/igd.c

@@ -349,8 +349,8 @@ static int vfio_pci_igd_lpc_init(VFIOPCIDevice *vdev,
 
 static bool vfio_pci_igd_setup_lpc_bridge(VFIOPCIDevice *vdev, Error **errp)
 {
-    g_autofree struct vfio_region_info *host = NULL;
+    struct vfio_region_info *host = NULL;
-    g_autofree struct vfio_region_info *lpc = NULL;
+    struct vfio_region_info *lpc = NULL;
     PCIDevice *lpc_bridge;
     int ret;
 
@@ -510,7 +510,7 @@ void vfio_probe_igd_bar0_quirk(VFIOPCIDevice *vdev, int nr)
 
 static bool vfio_pci_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
 {
-    g_autofree struct vfio_region_info *opregion = NULL;
+    struct vfio_region_info *opregion = NULL;
     int ret, gen;
     uint64_t gms_size = 0;
     uint64_t *bdsm_size;
@@ -551,7 +551,7 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
          * - OpRegion
          * - Same LPC bridge and Host bridge VID/DID/SVID/SSID as host
          */
-        g_autofree struct vfio_region_info *rom = NULL;
+        struct vfio_region_info *rom = NULL;
 
         legacy_mode_enabled = true;
         info_report("IGD legacy mode enabled, "
@@ -681,7 +681,7 @@ error:
  */
 static bool vfio_pci_kvmgt_config_quirk(VFIOPCIDevice *vdev, Error **errp)
 {
-    g_autofree struct vfio_region_info *opregion = NULL;
+    struct vfio_region_info *opregion = NULL;
     int gen;
 
     if (!vfio_pci_is(vdev, PCI_VENDOR_ID_INTEL, PCI_ANY_ID) ||

hw/vfio/pci.c

@@ -883,8 +883,8 @@ static void vfio_update_msi(VFIOPCIDevice *vdev)
 
 static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
 {
-    g_autofree struct vfio_region_info *reg_info = NULL;
     VFIODevice *vbasedev = &vdev->vbasedev;
+    struct vfio_region_info *reg_info = NULL;
     uint64_t size;
     off_t off = 0;
     ssize_t bytes;
@@ -2710,7 +2710,7 @@ static VFIODeviceOps vfio_pci_ops = {
 bool vfio_populate_vga(VFIOPCIDevice *vdev, Error **errp)
 {
     VFIODevice *vbasedev = &vdev->vbasedev;
-    g_autofree struct vfio_region_info *reg_info = NULL;
+    struct vfio_region_info *reg_info = NULL;
     int ret;
 
     ret = vfio_device_get_region_info(vbasedev, VFIO_PCI_VGA_REGION_INDEX, &reg_info);
@@ -2775,7 +2775,7 @@ bool vfio_populate_vga(VFIOPCIDevice *vdev, Error **errp)
 static bool vfio_populate_device(VFIOPCIDevice *vdev, Error **errp)
 {
     VFIODevice *vbasedev = &vdev->vbasedev;
-    g_autofree struct vfio_region_info *reg_info = NULL;
+    struct vfio_region_info *reg_info = NULL;
     struct vfio_irq_info irq_info;
     int i, ret = -1;
 

hw/vfio/region.c

@@ -182,7 +182,7 @@ static int vfio_setup_region_sparse_mmaps(VFIORegion *region,
 int vfio_region_setup(Object *obj, VFIODevice *vbasedev, VFIORegion *region,
                       int index, const char *name)
 {
-    g_autofree struct vfio_region_info *info = NULL;
+    struct vfio_region_info *info = NULL;
     int ret;
 
     ret = vfio_device_get_region_info(vbasedev, index, &info);

include/hw/vfio/vfio-device.h

@@ -83,6 +83,7 @@ typedef struct VFIODevice {
     IOMMUFDBackend *iommufd;
     VFIOIOASHwpt *hwpt;
     QLIST_ENTRY(VFIODevice) hwpt_next;
+    struct vfio_region_info **reginfo;
 } VFIODevice;
 
 struct VFIODeviceOps {