linux-kernel - Re: [kvm-devel] [PATCH 3/8] SVM: add module parameter to disable Nested Paging

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Date:	Fri, 25 Jan 2008 15:35:23 -0600
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH 3/8] SVM: add module parameter to disable
 Nested Paging

Joerg Roedel wrote:
> To disable the use of the Nested Paging feature even if it is available in
> hardware this patch adds a module parameter. Nested Paging can be disabled by
> passing npt=off to the kvm_amd module.
>
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kvm/svm.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 49bb57a..2e718ff 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -48,6 +48,9 @@ MODULE_LICENSE("GPL");
>  #define SVM_DEATURE_SVML (1 << 2)
>  
>  static bool npt_enabled = false;
> +static char *npt = "on";
> +
> +module_param(npt, charp, S_IRUGO);
>   

This would probably be better as an integer.  Then we don't have to do 
nasty things like implicitly cast a literal to a char *.

Regards,

Anthony Liguori

>  static void kvm_reput_irq(struct vcpu_svm *svm);
>  
> @@ -415,6 +418,11 @@ static __init int svm_hardware_setup(void)
>  	if (!svm_has(SVM_FEATURE_NPT))
>  		npt_enabled = false;
>  
> +	if (npt_enabled && strncmp(npt, "off", 3) == 0) {
> +		printk(KERN_INFO "kvm: Nested Paging disabled\n");
> +		npt_enabled = false;
> +	}
> +
>  	if (npt_enabled)
>  		printk(KERN_INFO "kvm: Nested Paging enabled\n");
>  
>   

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