From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 5/9] xen: arm: Handle CP15 register traps from userspace Date: Wed, 10 Sep 2014 11:56:09 -0700 Message-ID: <54109EC9.1070303@linaro.org> References: <1410279730.8217.238.camel@kazak.uk.xensource.com> <1410279788-27167-5-git-send-email-ian.campbell@citrix.com> <540F9062.8030904@linaro.org> <1410342483.8217.274.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1410342483.8217.274.camel@kazak.uk.xensource.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: stefano.stabellini@eu.citrix.com, tim@xen.org, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 10/09/14 02:48, Ian Campbell wrote: > 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. I would turn into an ASSERT to avoid checking it in non-debug build. Regards, -- Julien Grall