[PATCH 1/6] kdump: crash-time virt disable function

Avi Kivity avi at redhat.com
Thu Oct 30 09:50:31 EDT 2008

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.

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