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

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Date:	Wed, 05 Nov 2008 09:26:53 -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 15/16] kvm: x86: set kdump virt_disable function on initialization

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.

> +	if (r) {
> +		printk(KERN_ERR "kvm: virt_disable function already set?\n");
> +		goto out_clear_ops;
> +	}
> +
>  	r = kvm_mmu_module_init();
>  	if (r)
> -		goto out_clear_ops;
> +		goto out_clear_crash;
>  
>  	kvm_init_msr_list();
>  
> @@ -2617,6 +2631,8 @@ int kvm_arch_init(void *opaque)
>  			PT_DIRTY_MASK, PT64_NX_MASK, 0, 0);
>  	return 0;
>  
> +out_clear_crash:
> +	clear_virt_disable_func();
>  out_clear_ops:
>  	kvm_x86_ops = NULL;
>  out:
> @@ -2625,6 +2641,7 @@ out:
>  
>  void kvm_arch_exit(void)
>  {
> +	clear_virt_disable_func();
>  	kvm_x86_ops = NULL;
>  	kvm_mmu_module_exit();
>  }
> -- 
> 1.5.5.GIT
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