From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34294) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bYDbC-0001z2-EO for qemu-devel@nongnu.org; Fri, 12 Aug 2016 10:38:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bYDb7-0008J6-K4 for qemu-devel@nongnu.org; Fri, 12 Aug 2016 10:38:14 -0400 References: <1470591415-3268-1-git-send-email-nikunj@linux.vnet.ibm.com> <1470591415-3268-3-git-send-email-nikunj@linux.vnet.ibm.com> <1470605617.12584.182.camel@kernel.crashing.org> <20160809032817.GG9057@voom.fritz.box> <87invaa6fg.fsf@abhimanyu.i-did-not-set--mail-host-address--so-tickle-me> <87d1li9u85.fsf@abhimanyu.i-did-not-set--mail-host-address--so-tickle-me> <20160812062917.GT16493@voom.fritz.box> <87fuqa8p22.fsf@abhimanyu.i-did-not-set--mail-host-address--so-tickle-me> From: Thomas Huth Message-ID: <3c439ecd-57dc-eabe-fc68-d8c7cdce9e44@redhat.com> Date: Fri, 12 Aug 2016 09:29:26 +0200 MIME-Version: 1.0 In-Reply-To: <87fuqa8p22.fsf@abhimanyu.i-did-not-set--mail-host-address--so-tickle-me> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH 2/6] target-ppc: Implement darn instruction List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nikunj A Dadhania , David Gibson Cc: Ravi Bangoria , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, rth@twiddle.net On 12.08.2016 08:43, Nikunj A Dadhania wrote: > David Gibson writes: > >> [ Unknown signature status ] >> On Tue, Aug 09, 2016 at 02:47:46PM +0530, Nikunj A Dadhania wrote: >>> Nikunj A Dadhania writes: >>> >>>> David Gibson writes: >>>> >>>>> [ Unknown signature status ] >>>>> On Mon, Aug 08, 2016 at 07:33:37AM +1000, Benjamin Herrenschmidt wrote: >>>>>> On Sun, 2016-08-07 at 23:06 +0530, Nikunj A Dadhania wrote: >>>>>>> +target_ulong helper_darn(uint32_t l) >>>>>>> +{ >>>>>>> + target_ulong r = UINT64_MAX; >>>>>>> + >>>>>>> + if (l <= 2) { >>>>>>> + do { >>>>>>> + r = random() * random(); >>>>>>> + r &= l ? UINT64_MAX : UINT32_MAX; >>>>>>> + } while (r == UINT64_MAX); >>>>>>> + } >>>>>>> + >>>>>>> + return r; >>>>>>> +} >>>>>>> #endif >>>>>> >>>>>> Isn't this a bit week ? Look at the implementation of H_RANDOM... >>>>> >>>>> Indeed, you should be using the rng backend that H_RANDOM, virtio-rng >>>>> and the Intel random number instruction all use. >>> >>> Can you point me to the intel instruction, I couldn't get rdrand >>> implementation. >> >> Ah.. turns out no. I'd assumed it was there and used the same backend >> as virtio-rng and H_RANDOM, but I hadn't actually looked at the code, >> and now that I'm trying I can't see it either. >> >>> >>>> I was looking at implementing this, AFAIU, I have to get a new RNG >>>> object in the initialization routine. We would need an instance of this >>>> per machine. So for pseries I can add in ppc_spapr_init(). I am not sure >>>> in case of linux-user where should this be initialized. >>>> >>>> One other place was init_proc_POWER9(), but that will be per cpu and >>>> member of CPUPPCState structure. Advantage is it will work for system >>>> emulation and linux-user both and we would not need a lock. >>> >>> More issues here. Random backend is not compiled for linux-user, adding >>> that wasn't difficult, but then rng_backend_request_entropy() uses >>> qemu_set_fd_handler() which is a stub for linux-user >>> (stubs/set-fd-handler.c)7 >> >> >> Ah.. yeah, not sure how we'll need to handle that. > > I have sent updated patch, reading from /dev/random. Not sure if that is > allowed in tcg. Works fine though. You can not rely on /dev/random for this job, since it might block. So your guest would stop executing when there is not enough random data available in the host, and I think that's quite a bad behavior... Thomas