hw/i386/pc_sysfw: support two flash drives

This patch allows the user to usefully specify

  -drive file=img_1,if=pflash,format=raw,readonly \
  -drive file=img_2,if=pflash,format=raw

on the command line. The flash images will be mapped under 4G in their
reverse unit order -- that is, with their base addresses progressing
downwards, in increasing unit order.

(The unit number increases with command line order if not explicitly
specified.)

This accommodates the following use case: suppose that OVMF is split in
two parts, a writeable host file for non-volatile variable storage, and a
read-only part for bootstrap and decompressible executable code.

The binary code part would be read-only, centrally managed on the host
system, and passed in as unit 0. The variable store would be writeable,
VM-specific, and passed in as unit 1.

  00000000ffe00000-00000000ffe1ffff (prio 0, R-): system.flash1
  00000000ffe20000-00000000ffffffff (prio 0, R-): system.flash0

(If the guest tries to write to the flash range that is backed by the
read-only drive, pflash_update() is never called; various flash
programming/erase errors are returned to the guest instead. See the
callers of pflash_update(), and the initialization of "pfl->ro", in
"hw/block/pflash_cfi01.c".)

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/pc_sysfw.c

@@ -72,36 +72,103 @@ static void pc_isa_bios_init(MemoryRegion *rom_memory,
     memory_region_set_readonly(isa_bios, true);
 }
 
-static void pc_system_flash_init(MemoryRegion *rom_memory,
+#define FLASH_MAP_UNIT_MAX 2
-                                 DriveInfo *pflash_drv)
+
+/* We don't have a theoretically justifiable exact lower bound on the base
+ * address of any flash mapping. In practice, the IO-APIC MMIO range is
+ * [0xFEE00000..0xFEE01000[ -- see IO_APIC_DEFAULT_ADDRESS --, leaving free
+ * only 18MB-4KB below 4G. For now, restrict the cumulative mapping to 8MB in
+ * size.
+ */
+#define FLASH_MAP_BASE_MIN ((hwaddr)(0x100000000ULL - 8*1024*1024))
+
+/* This function maps flash drives from 4G downward, in order of their unit
+ * numbers. The mapping starts at unit#0, with unit number increments of 1, and
+ * stops before the first missing flash drive, or before
+ * unit#FLASH_MAP_UNIT_MAX, whichever is reached first.
+ *
+ * Addressing within one flash drive is of course not reversed.
+ *
+ * An error message is printed and the process exits if:
+ * - the size of the backing file for a flash drive is non-positive, or not a
+ *   multiple of the required sector size, or
+ * - the current mapping's base address would fall below FLASH_MAP_BASE_MIN.
+ *
+ * The drive with unit#0 (if available) is mapped at the highest address, and
+ * it is passed to pc_isa_bios_init(). Merging several drives for isa-bios is
+ * not supported.
+ */
+static void pc_system_flash_init(MemoryRegion *rom_memory)
 {
+    int unit;
+    DriveInfo *pflash_drv;
     BlockDriverState *bdrv;
     int64_t size;
-    hwaddr phys_addr;
+    char *fatal_errmsg = NULL;
+    hwaddr phys_addr = 0x100000000ULL;
     int sector_bits, sector_size;
     pflash_t *system_flash;
     MemoryRegion *flash_mem;
+    char name[64];
 
-    bdrv = pflash_drv->bdrv;
-    size = bdrv_getlength(pflash_drv->bdrv);
     sector_bits = 12;
     sector_size = 1 << sector_bits;
 
-    if ((size % sector_size) != 0) {
+    for (unit = 0;
-        fprintf(stderr,
+         (unit < FLASH_MAP_UNIT_MAX &&
-                "qemu: PC system firmware (pflash) must be a multiple of 0x%x\n",
+          (pflash_drv = drive_get(IF_PFLASH, 0, unit)) != NULL);
-                sector_size);
+         ++unit) {
+        bdrv = pflash_drv->bdrv;
+        size = bdrv_getlength(bdrv);
+        if (size < 0) {
+            fatal_errmsg = g_strdup_printf("failed to get backing file size");
+        } else if (size == 0) {
+            fatal_errmsg = g_strdup_printf("PC system firmware (pflash) "
+                               "cannot have zero size");
+        } else if ((size % sector_size) != 0) {
+            fatal_errmsg = g_strdup_printf("PC system firmware (pflash) "
+                               "must be a multiple of 0x%x", sector_size);
+        } else if (phys_addr < size || phys_addr - size < FLASH_MAP_BASE_MIN) {
+            fatal_errmsg = g_strdup_printf("oversized backing file, pflash "
+                               "segments cannot be mapped under "
+                               TARGET_FMT_plx, FLASH_MAP_BASE_MIN);
+        }
+        if (fatal_errmsg != NULL) {
+            Location loc;
+
+            /* push a new, "none" location on the location stack; overwrite its
+             * contents with the location saved in the option; print the error
+             * (includes location); pop the top
+             */
+            loc_push_none(&loc);
+            if (pflash_drv->opts != NULL) {
+                qemu_opts_loc_restore(pflash_drv->opts);
+            }
+            error_report("%s", fatal_errmsg);
+            loc_pop(&loc);
+            g_free(fatal_errmsg);
             exit(1);
         }
 
-    phys_addr = 0x100000000ULL - size;
+        phys_addr -= size;
-    system_flash = pflash_cfi01_register(phys_addr, NULL, "system.flash", size,
-                                         bdrv, sector_size, size >> sector_bits,
-                                         1, 0x0000, 0x0000, 0x0000, 0x0000, 0);
-    flash_mem = pflash_cfi01_get_memory(system_flash);
 
+        /* pflash_cfi01_register() creates a deep copy of the name */
+        snprintf(name, sizeof name, "system.flash%d", unit);
+        system_flash = pflash_cfi01_register(phys_addr, NULL /* qdev */, name,
+                                             size, bdrv, sector_size,
+                                             size >> sector_bits,
+                                             1      /* width */,
+                                             0x0000 /* id0 */,
+                                             0x0000 /* id1 */,
+                                             0x0000 /* id2 */,
+                                             0x0000 /* id3 */,
+                                             0      /* be */);
+        if (unit == 0) {
+            flash_mem = pflash_cfi01_get_memory(system_flash);
             pc_isa_bios_init(rom_memory, flash_mem, size);
         }
+    }
+}
 
 static void old_pc_system_rom_init(MemoryRegion *rom_memory, bool isapc_ram_fw)
 {
@@ -181,5 +248,5 @@ void pc_system_firmware_init(MemoryRegion *rom_memory, bool isapc_ram_fw)
         exit(1);
     }
 
-    pc_system_flash_init(rom_memory, pflash_drv);
+    pc_system_flash_init(rom_memory);
 }