From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eduardo Habkost Subject: Re: [PATCH 0/2] kvm: disable virtualization on kdump Date: Tue, 28 Oct 2008 17:45:30 -0200 Message-ID: <20081028194530.GK23893@blackpad> References: <4904676F.3020706@redhat.com> <490487C1.1010707@redhat.com> <20081026213927.GF23893@blackpad> <49058645.9010005@redhat.com> <20081027122808.GH23893@blackpad> <4905C9ED.807@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Andrew Morton , kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Haren Myneni , Simon Horman , Avi Kivity , Vivek Goyal To: "Eric W. Biederman" Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kexec-bounces-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Errors-To: kexec-bounces+glkk-kexec=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: kvm.vger.kernel.org On Mon, Oct 27, 2008 at 10:32:43AM -0700, Eric W. Biederman wrote: > Avi Kivity writes: > > > > I wouldn't mind notifiers (with a nice comment explaining that you must know > > what you're doing, though that's the case with most kernel APIs). I'm fine with > > either approach. > > This is the 3rd request I have seen for a notifier. This is the first > request I have seen for code that must be executed in the kexec on > panic path. So history suggest to me that notifiers make it > unreasonably easy to get code onto the kexec on panic code path. > > Occasionally the kexec on panic code path is tested to see how > well it works in strange situations like being called from > a stack overflow etc. > > The rest of the history is that previous attempts like lkcd > had very programmer friendly interfaces, that worked fine > in test environments giving beautiful core dumps, but when things > broke in the field they were essentially useless. The kdump > approach is still not completely reliable but it does work > well enough that people get useful crash dumps sometimes. > > I feel anything that makes the kexec on panic code path harder > to verify it will work when things are crazy broken, like > a notifier is something we should avoid. I am still wondering if a simple function pointer (instead of a full notifier interface) would be good enough. It looks like a reasonable tradeoff. I think I will get flamed if I try to pull to the core a bunch of code that always lived in the KVM module. 8) And even if we pull those functions to the core, we will still have a function pointer on the new code anyway, because we would need to support vmx and svm. -- Eduardo