[Qemu-devel] [PATCH] migration: avoid copying ignore-shared ramblock when in incoming migration

[Catherine Ho]

Commit 18269069c310 ("migration: Introduce ignore-shared capability") 
addes a ignore-shared capability to bypass the shared ramblock (e,g,
membackend + numa node). It does good to live migration.

This commit expected that QEMU doesn't write to guest RAM until 
VM starts, but it does on aarch64 qemu:
Backtrace:
1  0x000055f4a296dd84 in address_space_write_rom_internal () at exec.c:3458
2  0x000055f4a296de3a in address_space_write_rom () at exec.c:3479
3  0x000055f4a2d519ff in rom_reset () at hw/core/loader.c:1101
4  0x000055f4a2d475ec in qemu_devices_reset () at hw/core/reset.c:69
5  0x000055f4a2c90a28 in qemu_system_reset () at vl.c:1675
6  0x000055f4a2c9851d in main () at vl.c:4552

In address_space_write_rom_internal, if the ramblock is RAM of 
ramblock_is_ignored(), memcpy this ramblock will cause the memory-backend
file corruption.
But in normal case (!in_incoming_migration), this logic should be reserved.

Fixes: commit 18269069c310 ("migration: Introduce ignore-shared capability") 
Signed-off-by: Catherine Ho <address@hidden>
Suggested-by: Yury Kotov <address@hidden>
---
 exec.c                    | 4 ++++
 include/exec/cpu-common.h | 1 +
 include/qemu/option.h     | 1 +
 migration/ram.c           | 2 +-
 vl.c                      | 2 ++
 5 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/exec.c b/exec.c
index 86a38d3b3b..f08321fb7a 100644
--- a/exec.c
+++ b/exec.c
@@ -47,6 +47,7 @@
 #include "exec/address-spaces.h"
 #include "sysemu/xen-mapcache.h"
 #include "trace-root.h"
+#include "qemu/option.h"
 
 #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
 #include <linux/falloc.h>
@@ -3455,6 +3456,9 @@ static inline MemTxResult 
address_space_write_rom_internal(AddressSpace *as,
             l = memory_access_size(mr, l, addr1);
         } else {
             /* ROM/RAM case */
+            if (in_incoming_migration && ramblock_is_ignored(mr->ram_block)) {
+                break;
+            }
             ptr = qemu_map_ram_ptr(mr->ram_block, addr1);
             switch (type) {
             case WRITE_DATA:
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index cef8b88a2a..c80b7248a6 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -76,6 +76,7 @@ void *qemu_ram_get_host_addr(RAMBlock *rb);
 ram_addr_t qemu_ram_get_offset(RAMBlock *rb);
 ram_addr_t qemu_ram_get_used_length(RAMBlock *rb);
 bool qemu_ram_is_shared(RAMBlock *rb);
+bool ramblock_is_ignored(RAMBlock *block);
 bool qemu_ram_is_uf_zeroable(RAMBlock *rb);
 void qemu_ram_set_uf_zeroable(RAMBlock *rb);
 bool qemu_ram_is_migratable(RAMBlock *rb);
diff --git a/include/qemu/option.h b/include/qemu/option.h
index 844587cab3..7509435164 100644
--- a/include/qemu/option.h
+++ b/include/qemu/option.h
@@ -139,4 +139,5 @@ QemuOptsList *qemu_opts_append(QemuOptsList *dst, 
QemuOptsList *list);
 QDict *keyval_parse(const char *params, const char *implied_key,
                     Error **errp);
 
+extern bool in_incoming_migration;
 #endif
diff --git a/migration/ram.c b/migration/ram.c
index 35bd6213e9..d6de9d335d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -159,7 +159,7 @@ out:
     return ret;
 }
 
-static bool ramblock_is_ignored(RAMBlock *block)
+bool ramblock_is_ignored(RAMBlock *block)
 {
     return !qemu_ram_is_migratable(block) ||
            (migrate_ignore_shared() && qemu_ram_is_shared(block));
diff --git a/vl.c b/vl.c
index c1d5484e12..b79aec9ac3 100644
--- a/vl.c
+++ b/vl.c
@@ -145,6 +145,7 @@ bool enable_cpu_pm = false;
 int nb_nics;
 NICInfo nd_table[MAX_NICS];
 int autostart;
+bool in_incoming_migration;
 static enum {
     RTC_BASE_UTC,
     RTC_BASE_LOCALTIME,
@@ -3797,6 +3798,7 @@ int main(int argc, char **argv, char **envp)
                     runstate_set(RUN_STATE_INMIGRATE);
                 }
                 incoming = optarg;
+                in_incoming_migration = true;
                 break;
             case QEMU_OPTION_only_migratable:
                 /*
-- 
2.17.1