From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 3/4] xen/arm: Implement a dummy debug monitor for ARM32 Date: Fri, 02 May 2014 14:29:45 +0100 Message-ID: <53639DC9.2060007@linaro.org> References: <1398379556-1132-1-git-send-email-julien.grall@linaro.org> <1398379556-1132-4-git-send-email-julien.grall@linaro.org> <1399028953.32736.42.camel@kazak.uk.xensource.com> <53639561.3070303@linaro.org> <1399036479.5226.6.camel@kazak.uk.xensource.com> 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 1WgDXB-0001PX-8w for xen-devel@lists.xenproject.org; Fri, 02 May 2014 13:29:49 +0000 Received: by mail-ee0-f51.google.com with SMTP id c13so3148992eek.24 for ; Fri, 02 May 2014 06:29:47 -0700 (PDT) In-Reply-To: <1399036479.5226.6.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: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com List-Id: xen-devel@lists.xenproject.org On 05/02/2014 02:14 PM, Ian Campbell wrote: > On Fri, 2014-05-02 at 13:53 +0100, Julien Grall wrote: >> On 05/02/2014 12:09 PM, Ian Campbell wrote: >>> On Thu, 2014-04-24 at 23:45 +0100, Julien Grall wrote: >>>> XSA-93 (commit 0b18220 "xen/arm: Don't let guess access to Debug and Performance >>>> Monitors registers") disable Debug Registers access. >>>> >>>> When CONFIG_PERF_EVENTS is enabled in the Linux Kernel, it will try to >>>> initialize the debug monitors. If an error occured Linux won't use this >>>> feature. >>>> >>>> The implementation made Xen expose a minimal set of registers which let think >>>> the guest (i.e.) thinks HW debug won't work. >>> >>> Why only for arm32? >> >> Because, if I'm not mistaken, you've already implemented a dummy HW >> debug for arm64 in commit 0b182202 "xen/arm: Don't let guess access to >> Debug and Performance Monitor registers". > > That's a RAZ/WI thing, I thought this was something cleverer (returing > values to make the guest think nothing was there). Most of the time RAZ/WI is enough. The arm32 implementation makes the life harder. I didn't check the arm64 implementation as I don't use it every day... I need to set up the Foundation Model on my computer. -- Julien Grall