loader: store FW CFG ROM files in RAM

ROM files that are put in FW CFG are copied to guest ram, by BIOS, but
they are not backed by RAM so they don't get migrated.

Each time we change two bytes in such a ROM this breaks cross-version
migration: since we can migrate after BIOS has read the first byte but
before it has read the second one, getting an inconsistent state.

Future-proof this by creating, for each such ROM,
an MR serving as the backing store.
This MR is never mapped into guest memory, but it's registered
as RAM so it's migrated with the guest.

Naturally, this only helps for -M 1.7 and up, older machine types
will still have the cross-version migration bug.
Luckily the race window for the problem to trigger is very small,
which is also likely why we didn't notice the cross-version
migration bug in testing yet.

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

diff --git a/hw/core/loader.c b/hw/core/loader.c
index 6875b7ecf354c630b0c52a7e5e5631cc56ecd64e..7b3d3ee6a0dbfaa54e6ded0fdf44328da928b06b 100644 (file)
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -54,6 +54,8 @@
 
 #include <zlib.h>
 
+bool rom_file_in_ram = true;
+
 static int roms_loaded;
 
 /* return the size or -1 if error */
@@ -576,6 +578,7 @@ struct Rom {
     size_t datasize;
 
     uint8_t *data;
+    MemoryRegion *mr;
     int isrom;
     char *fw_dir;
     char *fw_file;
@@ -605,6 +608,21 @@ static void rom_insert(Rom *rom)
     QTAILQ_INSERT_TAIL(&roms, rom, next);
 }
 
+static void *rom_set_mr(Rom *rom, Object *owner, const char *name)
+{
+    void *data;
+
+    rom->mr = g_malloc(sizeof(*rom->mr));
+    memory_region_init_ram(rom->mr, owner, name, rom->datasize);
+    memory_region_set_readonly(rom->mr, true);
+    vmstate_register_ram_global(rom->mr);
+
+    data = memory_region_get_ram_ptr(rom->mr);
+    memcpy(data, rom->data, rom->datasize);
+
+    return data;
+}
+
 int rom_add_file(const char *file, const char *fw_dir,
                  hwaddr addr, int32_t bootindex)
 {
@@ -646,6 +664,7 @@ int rom_add_file(const char *file, const char *fw_dir,
     if (rom->fw_file && fw_cfg) {
         const char *basename;
         char fw_file_name[56];
+        void *data;
 
         basename = strrchr(rom->fw_file, '/');
         if (basename) {
@@ -655,8 +674,15 @@ int rom_add_file(const char *file, const char *fw_dir,
         }
         snprintf(fw_file_name, sizeof(fw_file_name), "%s/%s", rom->fw_dir,
                  basename);
-        fw_cfg_add_file(fw_cfg, fw_file_name, rom->data, rom->romsize);
         snprintf(devpath, sizeof(devpath), "/rom@%s", fw_file_name);
+
+        if (rom_file_in_ram) {
+            data = rom_set_mr(rom, OBJECT(fw_cfg), devpath);
+        } else {
+            data = rom->data;
+        }
+
+        fw_cfg_add_file(fw_cfg, fw_file_name, data, rom->romsize);
     } else {
         snprintf(devpath, sizeof(devpath), "/rom@" TARGET_FMT_plx, addr);
     }
@@ -731,7 +757,12 @@ static void rom_reset(void *unused)
         if (rom->data == NULL) {
             continue;
         }
-        cpu_physical_memory_write_rom(rom->addr, rom->data, rom->datasize);
+        if (rom->mr) {
+            void *host = memory_region_get_ram_ptr(rom->mr);
+            memcpy(host, rom->data, rom->datasize);
+        } else {
+            cpu_physical_memory_write_rom(rom->addr, rom->data, rom->datasize);
+        }
         if (rom->isrom) {
             /* rom needs to be written only once */
             g_free(rom->data);
@@ -781,6 +812,9 @@ static Rom *find_rom(hwaddr addr)
         if (rom->fw_file) {
             continue;
         }
+        if (rom->mr) {
+            continue;
+        }
         if (rom->addr > addr) {
             continue;
         }
@@ -808,6 +842,9 @@ int rom_copy(uint8_t *dest, hwaddr addr, size_t size)
         if (rom->fw_file) {
             continue;
         }
+        if (rom->mr) {
+            continue;
+        }
         if (rom->addr + rom->romsize < addr) {
             continue;
         }
@@ -866,7 +903,13 @@ void do_info_roms(Monitor *mon, const QDict *qdict)
     Rom *rom;
 
     QTAILQ_FOREACH(rom, &roms, next) {
-        if (!rom->fw_file) {
+        if (rom->mr) {
+            monitor_printf(mon, "%s"
+                           " size=0x%06zx name=\"%s\"\n",
+                           rom->mr->name,
+                           rom->romsize,
+                           rom->name);
+        } else if (!rom->fw_file) {
             monitor_printf(mon, "addr=" TARGET_FMT_plx
                            " size=0x%06zx mem=%s name=\"%s\"\n",
                            rom->addr, rom->romsize,

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 46f1fd7ffa6e5b0feda23faf9a378ff8ae314b39..4591027ce5496138d4a519c977e15f6611e574a5 100644 (file)
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -25,6 +25,7 @@
 #include <glib.h>
 
 #include "hw/hw.h"
+#include "hw/loader.h"
 #include "hw/i386/pc.h"
 #include "hw/i386/apic.h"
 #include "hw/pci/pci.h"
@@ -252,6 +253,7 @@ static void pc_init_pci(QEMUMachineInitArgs *args)
 static void pc_init_pci_1_6(QEMUMachineInitArgs *args)
 {
     has_pci_info = false;
+    rom_file_in_ram = false;
     pc_init_pci(args);
 }
 

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index ab0aa70b712684a880f252f09c7c17ab746c1779..533a2d6769e6181d67e29a329ef5ac14123c1c0c 100644 (file)
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -28,6 +28,7 @@
  * THE SOFTWARE.
  */
 #include "hw/hw.h"
+#include "hw/loader.h"
 #include "sysemu/arch_init.h"
 #include "hw/i2c/smbus.h"
 #include "hw/boards.h"
@@ -221,6 +222,7 @@ static void pc_q35_init(QEMUMachineInitArgs *args)
 static void pc_q35_init_1_6(QEMUMachineInitArgs *args)
 {
     has_pci_info = false;
+    rom_file_in_ram = false;
     pc_q35_init(args);
 }
 

diff --git a/include/hw/loader.h b/include/hw/loader.h
index eb9c9a361265c11f70c86a8934ec840785c1e096..61457360f6bfcf0c550844681c692b9dbc394b34 100644 (file)
--- a/include/hw/loader.h
+++ b/include/hw/loader.h
@@ -36,6 +36,7 @@ void pstrcpy_targphys(const char *name,
                       hwaddr dest, int buf_size,
                       const char *source);
 
+extern bool rom_file_in_ram;
 
 int rom_add_file(const char *file, const char *fw_dir,
                  hwaddr addr, int32_t bootindex);