From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60613) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UzRhy-0000g3-UB for qemu-devel@nongnu.org; Wed, 17 Jul 2013 09:23:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UzRhu-0003Y8-LW for qemu-devel@nongnu.org; Wed, 17 Jul 2013 09:23:54 -0400 Received: from mail-pb0-x234.google.com ([2607:f8b0:400e:c01::234]:51553) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UzRhu-0003Y2-Ex for qemu-devel@nongnu.org; Wed, 17 Jul 2013 09:23:50 -0400 Received: by mail-pb0-f52.google.com with SMTP id xa12so1882207pbc.25 for ; Wed, 17 Jul 2013 06:23:49 -0700 (PDT) Sender: Richard Henderson Message-ID: <51E69AE1.1060809@twiddle.net> Date: Wed, 17 Jul 2013 06:23:45 -0700 From: Richard Henderson MIME-Version: 1.0 References: <1373840171-25556-1-git-send-email-rth@twiddle.net> <1373840171-25556-4-git-send-email-rth@twiddle.net> <8761w9wm50.fsf@blackfin.pond.sub.org> <51E67B7A.8000800@redhat.com> In-Reply-To: <51E67B7A.8000800@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: aliguori@us.ibm.com, Gerd Hoffmann , Markus Armbruster , qemu-devel@nongnu.org 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~