From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39571) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VncWt-0007IZ-Hq for qemu-devel@nongnu.org; Mon, 02 Dec 2013 18:03:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VncWm-0006fQ-8J for qemu-devel@nongnu.org; Mon, 02 Dec 2013 18:03:51 -0500 Received: from mail-pa0-f54.google.com ([209.85.220.54]:45041) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VncWm-0006ez-2q for qemu-devel@nongnu.org; Mon, 02 Dec 2013 18:03:44 -0500 Received: by mail-pa0-f54.google.com with SMTP id rd3so2036534pab.27 for ; Mon, 02 Dec 2013 15:03:42 -0800 (PST) Message-ID: <529D11C5.2080505@ozlabs.ru> Date: Tue, 03 Dec 2013 10:03:33 +1100 From: Alexey Kardashevskiy MIME-Version: 1.0 References: <1385350750-21468-1-git-send-email-aik@ozlabs.ru> <529CBE15.8010206@msgid.tls.msk.ru> <529D0533.7090402@suse.de> In-Reply-To: <529D0533.7090402@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [Qemu-trivial] [PATCH] vl: remove (max_cpus > 255) check from smp_parse List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= , Michael Tokarev Cc: qemu-trivial@nongnu.org, Igor Mammedov , qemu-devel@nongnu.org, Eduardo Habkost On 12/03/2013 09:09 AM, Andreas Färber wrote: > Am 02.12.2013 18:06, schrieb Michael Tokarev: >> 25.11.2013 07:39, Alexey Kardashevskiy wrote: >>> Since modern POWER7/POWER8 chips can have more that 256 CPU threads >>> (>2000 actually), remove this check from smp_parse. >>> >>> The CPUs number is still checked against machine->max_cpus and this check >>> should be enough not to break other archs. > > "should be" is not exactly the highest level of confidence for a > "trivial" patch... :/ > >> [] >>> - if (max_cpus > 255) { >>> - fprintf(stderr, "Unsupported number of maxcpus\n"); >>> - exit(1); >>> - } > > I believe Eduardo touched that code last for NUMA, so let's CC him. > >> I don't know whenever this is actually safe. Do we have any static arrays >> of size 255 somewhere, which will be overflowed without this check? :) > > s390 has the ipi_states[] array, but not fixed to that size. s390 machines have QemuMachine::max_cpus == 255. > x86 APIC IDs I think have or had a limitation to 255 rather than 16-bit? > Igor? > > Alexey, did you actually check that, e.g., x86 machines don't break with > 256 or 257 CPUs now? PC_DEFAULT_MACHINE_OPTIONS sets it to 255. And I cannot find any machine which would not define max_cpus, have I missed any? -- Alexey