On Mon, 29 Jul 2019 at 22:47, Paolo Bonzini <pbonz...@redhat.com> wrote: > > The race is as follows: > > 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 > > and the second write is missed by the reader. > > 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 <dgilb...@redhat.com> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > --- > I tested this some time ago, and enough has changed that I don't > really trust those old results. Nevertheless, I am throwing out > the patch so that it is not forgotten.
This patch looks almost the same (maybe identical except for the commit message title?) as the patch "memory: introduce memory_global_after_dirty_log_sync" which you sent out at almost the same time as this one. Which patch should we be reviewing? thanks -- PMM
