Aligned 8-byte memory writes by a 64-bit target on a 64-bit host should
always turn into atomic 8-byte writes on the host, however if we missed
in the softmmu, and the TLB line was marked as not dirty, then we
would end up tearing the 8-byte write into two 4-byte writes in
access_with_adjusted_size().

Signed-off-by: Andrew Baumann <Andrew.Baumann@microsoft.com>
Message-Id: <20171013181913.7556-1-Andrew.Baumann@microsoft.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>