From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH] xen/arm: Init traps very early Date: Wed, 28 May 2014 15:04:45 +0100 Message-ID: <5385ECFD.5080702@citrix.com> References: <1401283983-19843-1-git-send-email-julien.grall@linaro.org> <5385E956.1040104@citrix.com> <5385EB80.5050905@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WpeTL-00072L-BO for xen-devel@lists.xenproject.org; Wed, 28 May 2014 14:04:51 +0000 In-Reply-To: <5385EB80.5050905@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: naresh.bhat@linaro.org, xen-devel@lists.xenproject.org, stefano.stabellini@citrix.com, ian.campbell@citrix.com, tim@xen.org List-Id: xen-devel@lists.xenproject.org On 28/05/14 14:58, Julien Grall wrote: > Hi Andrew, > > On 05/28/2014 02:49 PM, Andrew Cooper wrote: >> On 28/05/14 14:33, Julien Grall wrote: >>> The function init_traps setups the handler taken when Xen hits a BUG_ON/ASSERT. >>> >>> If an error happen before init_traps is called, we loose the backtrace. >>> >>> As the function doesn't require any specific setup, we can call it just >>> after Xen has jumped in C code. >>> >>> Signed-off-by: Julien Grall >>> --- >>> xen/arch/arm/setup.c | 3 +-- >>> 1 file changed, 1 insertion(+), 2 deletions(-) >>> >>> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c >>> index b9ce7a9..5bf8686 100644 >>> --- a/xen/arch/arm/setup.c >>> +++ b/xen/arch/arm/setup.c >>> @@ -666,6 +666,7 @@ void __init start_xen(unsigned long boot_phys_offset, >>> struct domain *dom0; >>> >>> setup_cache(); >>> + init_traps(); >> Having recently redone this in x86, it must be after >> set_processor_id(0), set_current() for debug sanity, and after >> percpu_init_areas() for future proofing. > Even though it doesn't harm to call before (the stack will be > corrupted), I agree to call init_traps after set_processor_id(0), and > therefore percpu_init_areas. > > But we don't need to have set_current correctly set up. The trap entries > won't save anything about the guest if the exception are taken from HYP > mode. > set_current((struct vcpu *)0xfffff000); /* debug sanity */ This is designed to force a pagefault if a trap handler tries to use current before current is a valid vcpu. It is a debugging measure rather than a functional one, and does pick up issues. ~Andrew