From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH 5/9] xen: arm: Handle CP15 register traps from userspace Date: Wed, 10 Sep 2014 10:48:03 +0100 Message-ID: <1410342483.8217.274.camel@kazak.uk.xensource.com> References: <1410279730.8217.238.camel@kazak.uk.xensource.com> <1410279788-27167-5-git-send-email-ian.campbell@citrix.com> <540F9062.8030904@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <540F9062.8030904@linaro.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Julien Grall Cc: stefano.stabellini@eu.citrix.com, tim@xen.org, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Tue, 2014-09-09 at 16:42 -0700, Julien Grall wrote: > Hi Ian, > > On 09/09/14 09:23, Ian Campbell wrote: > > Previously userspace access to PM* would have been incorrectly (but benignly) > > implemented as RAZ/WI when running on a 32-bit kernel and would cause a > > hypervisor exception (host crash) when running a 64-bit kernel (this was > > already solved via the fix to XSA-102). > > > > CLIDR, CCSIDR, DCCISW, ACTLR, PMINTENSET, PMINTENCLR are EL1 only, attempts to > > access from EL0 will trap to EL1 not to us, hence BUG_ON is appropriate now. > > In the unlikely case it happens, I don't think it will harm Xen, but > only the guest. So is the BUG_ON really necessary on these registers? > > I think we should use BUG_ON when we know that it will harm the Xen and > it's not possible to come back from the state. AIUI it would be a hardware bug to see these traps in Xen. I think a BUG_ON is acceptable for such an occurrence. Ian.