On 07/17/2013 04:09 AM, Paolo Bonzini wrote: >> >> Fails for me: >> >> qemu-system-x86_64: /work/armbru/qemu/exec.c:1927: memory_access_size: >> Assertion `l >= access_size_min' failed. > > This: > > unsigned access_size_min = mr->ops->impl.min_access_size; > unsigned access_size_max = mr->ops->impl.max_access_size; > > must be respectively: > > unsigned access_size_min = 1; > unsigned access_size_max = mr->ops->valid.max_access_size; > > access_size_min can be 1 because erroneous accesses must not crash > QEMU, they should trigger exceptions in the guest or just return > garbage (depending on the CPU). I'm not sure I understand the comment, > placing a 4-byte field at the last byte of a region makes no sense > (unless impl.unaligned is true). > > access_size_max can be mr->ops->valid.max_access_size because memory.c > can and will still break accesses bigger than > mr->ops->impl.max_access_size. > > Markus, can you try the minimal patch above? Or this one that also > does the consequent simplifications.
NAK. If you remove the check here, you're just trading it for one in the device. The device told you that it can't support a 1 byte read. (Either that, or the device incorrectly reported what it can actually do.) The proper fix is to change the interface of memory_access_size such that it can report errors. Indeed, very likely we should change it and its callers to also support over-sized reads, like access_with_adjusted_size in memory.c. r~
