From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 1/6] kdump: crash-time virt disable function
Date: Thu, 30 Oct 2008 15:50:31 +0200
Message-ID: <4909BBA7.1020307@redhat.com>
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Cc: Andrew Morton <akpm-3NddpPZAyC0@public.gmane.org>, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Haren Myneni <hbabu-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>,
	Simon Horman <horms-/R6kz+dDXgpPR4JQBCEnsQ@public.gmane.org>,
	"Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>,
	Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Eduardo Habkost <ehabkost-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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Eduardo Habkost wrote:
> This patch adds an interface to set a function to be called on crash time,
> on each CPU. The function will be set by code that enables virtualization
> extensions on the CPUs (i.e. KVM).  It will be called once on each CPU
> by machine_crash_shutdown(), and should do the very least to disable
> virt extensions on the CPU where it is being called.
>
> The function will be used by KVM to disable virtualization before halting
> the CPUs, otherwise the booting of the kdump kernel may hang. It does
> hang, when vmx is enabled, and I wouldn't be surprised if having svm
> enabled also causes problems.
>
> The functions that set the function pointer uses RCU synchronization,
> just in case the crash NMI is triggered while KVM is unloading.
>
> We can't just use the same notifiers used at reboot time (that are used
> by non-crash-dump kexec), because at crash time some CPUs may have IRQs
> disabled, so we can't use IPIs. The crash shutdown code use NMIs to
> tell the other CPUs to be halted, so the notifier call is hooked into
> the CPU halting code that is on the crash shutdown NMI handler.
>
> +static void (*virt_disable_fn)(unsigned int cpu);
>   

Since you never use the cpu argument, I suggest dropping it.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.