path: root/migration
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authorPaolo Bonzini <pbonzini@redhat.com>2018-02-06 18:37:39 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2019-08-20 17:26:20 +0200
commit9458a9a1df1a4c719e24512394d548c1fc7abd22 (patch)
tree2e7dd0685486a403fda9fb52c70406a04637ef8b /migration
parent1e8a98b53867f61da9ca09f411288e2085d323c4 (diff)
memory: fix race between TCG and accesses to dirty bitmap
There is a race between TCG and accesses to the dirty log: vCPU thread reader thread ----------------------- ----------------------- TLB check -> slow path notdirty_mem_write write to RAM set dirty flag clear dirty flag TLB check -> fast path read memory write to RAM Fortunately, in order to fix it, no change is required to the vCPU thread. However, the reader thread must delay the read after the vCPU thread has finished the write. This can be approximated conservatively by run_on_cpu, which waits for the end of the current translation block. A similar technique is used by KVM, which has to do a synchronous TLB flush after doing a test-and-clear of the dirty-page flags. Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'migration')
1 files changed, 1 insertions, 0 deletions
diff --git a/migration/ram.c b/migration/ram.c
index 35552c090b..b01a37e7ca 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1857,6 +1857,7 @@ static void migration_bitmap_sync(RAMState *rs)
+ memory_global_after_dirty_log_sync();
end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);