linux-kernel - Re: [PATCH 15/16] kvm: x86: set kdump virt

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Date:	Wed, 5 Nov 2008 15:50:05 -0200
From:	Eduardo Habkost <ehabkost@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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 15/16] kvm: x86: set kdump virt_disable function on
	initialization

On Wed, Nov 05, 2008 at 09:26:53AM -0800, Eric W. Biederman wrote:
> Eduardo Habkost <ehabkost@...hat.com> writes:
> 
> > Finally implement the virt_disable function for kdump. It will call
> > kvm_x86_ops->crash_hardware_disable(), that will disable virtualization
> > extensions on the CPU if it is not disabled yet.
> >
> > Signed-off-by: Eduardo Habkost <ehabkost@...hat.com>
> > ---
> >  arch/x86/kvm/x86.c |   19 ++++++++++++++++++-
> >  1 files changed, 18 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 049c6a0..9e61baf 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -40,6 +40,7 @@
> >  #include <asm/msr.h>
> >  #include <asm/desc.h>
> >  #include <asm/mtrr.h>
> > +#include <asm/virtext.h>
> >  
> >  #define MAX_IO_MSRS 256
> >  #define CR0_RESERVED_BITS						\
> > @@ -2581,6 +2582,13 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, struct
> > kvm_run *run, int in,
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_emulate_pio_string);
> >  
> > +/* Called at crash time, so we can disable virtualization if needed
> > + */
> > +static void crash_hardware_disable(void)
> > +{
> > +	kvm_x86_ops->crash_hardware_disable(NULL);
> > +}
> > +
> >  int kvm_arch_init(void *opaque)
> >  {
> >  	int r;
> > @@ -2605,9 +2613,15 @@ int kvm_arch_init(void *opaque)
> >  
> >  	kvm_x86_ops = ops;
> >  
> > +	r = set_virt_disable_func(crash_hardware_disable);
> 
> Can we make this say:
> set_virt_disable_func(kvm_x86_ops->crash_hardware_disable);
> 
> So we can avoid going through 2 levels of function pointers?
> I find that a little scary in code that might be running
> at the edge of stack overflow.

When I've checked this (on x86_64), gcc did tail recursion optimization
and the call was just a jump to the function, so stack usage shouldn't
be a problem.

But I am inclined to agree with you about the excess of abstraction.

-- 
Eduardo
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