From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 04/10] xen/arm: vgic-v3: Don't check the size when we ignore the write/read as zero Date: Wed, 21 Jan 2015 12:28:37 +0000 Message-ID: <54BF9B75.5030100@linaro.org> References: <1421684957-29884-1-git-send-email-julien.grall@linaro.org> <1421684957-29884-5-git-send-email-julien.grall@linaro.org> <1421769455.10440.306.camel@citrix.com> <54BE9341.7010307@linaro.org> <1421776670.10440.330.camel@citrix.com> <54BEA393.5060207@linaro.org> <1421842295.13271.16.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YDuPG-0000m1-Hv for xen-devel@lists.xenproject.org; Wed, 21 Jan 2015 12:29:10 +0000 Received: by mail-wi0-f176.google.com with SMTP id em10so16150227wid.3 for ; Wed, 21 Jan 2015 04:29:06 -0800 (PST) In-Reply-To: <1421842295.13271.16.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com List-Id: xen-devel@lists.xenproject.org On 21/01/15 12:11, Ian Campbell wrote: > I thought about this overnight, and I would like to keep UNPREDICATABLE > as the current log + crash please. Apart from the fact that I don't want > guests to be able to rely on unpredictable accesses returning 0 it is > also more consistent with the ARM ARM which says "UNPREDICTABLE > behaviour must not be documented or promoted as having a defined > effect". I was actually planning to suggest this as the access for each registers are clearly define in the specs. > So, in summary: > > 1) Any access which is described as UNPREDICTABLE in GIC spec 5.1.3 > should result in the current bad_width behaviour, that is: a log message > and a domain crash. Ok. > > 2) Accesses which are valid and which are correctly emulated according > to the features which our virtual GIC exposes to the guest should > succeed silently, regardless of whether that means WI, read a constant > or actually have some effect. Ok. > > 3) Accesses which are valid but which do not correctly emulate according > to the features of the virtual gic which we are exposing can log if we > think it is useful to do so. I gave a look to the code. We have few registers we don't correctly emulate. The current behavior seems to be inconsistent, we either inject a data abort (such as ICPENDR) or ignore the error (such as ICACTIVER). Shall we take a domain_crash approach (as bad_width) or inject a data abort? Regards, -- Julien Grall