From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x234.google.com (mail-pg0-x234.google.com [IPv6:2607:f8b0:400e:c05::234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 400vvh0tBPzDrRX for ; Tue, 13 Mar 2018 23:54:55 +1100 (AEDT) Received: by mail-pg0-x234.google.com with SMTP id i14so7908809pgv.3 for ; Tue, 13 Mar 2018 05:54:55 -0700 (PDT) Date: Tue, 13 Mar 2018 22:54:38 +1000 From: Nicholas Piggin To: Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 03/14] powerpc/64s: allocate lppacas individually Message-ID: <20180313225438.0c853b89@roar.ozlabs.ibm.com> In-Reply-To: <87woygf8qd.fsf@concordia.ellerman.id.au> References: <20180213150824.27689-1-npiggin@gmail.com> <20180213150824.27689-4-npiggin@gmail.com> <87woygf8qd.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 13 Mar 2018 23:41:46 +1100 Michael Ellerman wrote: > Nicholas Piggin writes: > > > diff --git a/arch/powerpc/platforms/pseries/kexec.c b/arch/powerpc/platforms/pseries/kexec.c > > index eeb13429d685..3fe126796975 100644 > > --- a/arch/powerpc/platforms/pseries/kexec.c > > +++ b/arch/powerpc/platforms/pseries/kexec.c > > @@ -23,7 +23,12 @@ > > > > void pseries_kexec_cpu_down(int crash_shutdown, int secondary) > > { > > - /* Don't risk a hypervisor call if we're crashing */ > > + /* > > + * Don't risk a hypervisor call if we're crashing > > + * XXX: Why? The hypervisor is not crashing. It might be better > > + * to at least attempt unregister to avoid the hypervisor stepping > > + * on our memory. > > + */ > > Because every extra line of code we run in the crashed kernel is another > opportunity to screw up and not make it into the kdump kernel. > > For example the hcalls we do to unregister the VPA might trigger hcall > tracing which runs a bunch of code and might trip up on something. We > could modify those hcalls to not be traced, but then we can't trace them > in normal operation. We really make no other hcalls in a crash? I didn't think of that. > > And the hypervisor might continue to write to the VPA, but that's OK > because it's the VPA of the crashing kernel, the kdump kernel runs in a > separate reserved memory region. Well that takes care of that concern. > Possibly we could fix the hcall tracing issues etc, but this code has > not given us any problems for quite a while (~13 years) - ie. there > seems to be no issue with re-registering the VPAs etc. in the kdump > kernel. No I think it's okay then, if you could drop that hunk... Thanks, Nick