linux-kernel - Re: [PATCH 08/16] x86: Emergency virtualization disable function

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Date:	Wed, 05 Nov 2008 09:33:06 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Eduardo Habkost <ehabkost@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Simon Horman <horms@...ge.net.au>,
	Andrew Morton <akpm@...l.org>, Vivek Goyal <vgoyal@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	Andrey Borzenkov <arvidjaar@...l.ru>, mingo@...hat.com,
	"Rafael J. Wysocki" <rjw@...k.pl>, kexec@...ts.infradead.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/16] x86: Emergency virtualization disable function

Eduardo Habkost <ehabkost@...hat.com> writes:

> +int set_virt_disable_func(void (*fn)(void))
> +{
> +	int r = 0;
> +
> +	spin_lock(&virt_disable_lock);
> +	if (!virt_disable_fn)
> +		rcu_assign_pointer(virt_disable_fn, fn);
> +	else
> +		r = -EEXIST;
> +	spin_unlock(&virt_disable_lock);
> +
> +	return r;
> +}
> +EXPORT_SYMBOL(set_virt_disable_func);

EXPORT_SYMBOL_GPL?

> +EXPORT_SYMBOL(clear_virt_disable_func);
EXPORT_SYMBOL_GPL?

We are talking a core internal api that should not even
be exported if KVM is compiled into the kernel.

I have had to tell people NO too many times by that
wanted to shove code on the kexec on panic path that
had no business there.  I do not want to give
the least little impression that this is an ok hook
for the to use.  The very specific name helps in
that regard thank you for that.  Having the symbol
exported GPL would help even more.

Overall I think the code is just barely ok.

I don't like the fact that to run 2-3 instructions per cpu we are two
function pointers deep.  It feels like we have an excess of
abstraction here on the kvm side.

Is it possible to have the individual kvm modules call
set_virt_disable_func and clear_virt_disable_func?  Instead
of going through the x86_kvm_ops?

It really feels like we have an excess of abstraction here.

Eric
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