From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Deegan <tim@xen.org>
Subject: Re: [PATCH 08/10] VMX: disable PML in vmx_vcpu_destroy
Date: Thu, 9 Apr 2015 13:04:39 +0100
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References: <1427423754-11841-1-git-send-email-kai.huang@linux.intel.com>
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To: Kai Huang <kai.huang@linux.intel.com>
Cc: yang.z.zhang@intel.com, andrew.cooper3@citrix.com, kevin.tian@intel.com, jbeulich@suse.com, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

At 10:35 +0800 on 27 Mar (1427452552), Kai Huang wrote:
> It's possible domain still remains in log-dirty mode when it is about to be
> destroyed, in which case we should manually disable PML for it.
> 
> Signed-off-by: Kai Huang <kai.huang@linux.intel.com>
> ---
>  xen/arch/x86/hvm/vmx/vmx.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index fce3aa2..75ac44b 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -153,6 +153,15 @@ static int vmx_vcpu_initialise(struct vcpu *v)
>  
>  static void vmx_vcpu_destroy(struct vcpu *v)
>  {
> +    /*
> +     * There are cases that domain still remains in log-dirty mode when it is
> +     * about to be destroyed (ex, user types 'xl destroy <dom>'), in which case
> +     * we should disable PML manually here. Note that vmx_vcpu_destroy is called
> +     * prior to vmx_domain_destroy so we need to disable PML for each vcpu
> +     * separately here.
> +     */
> +    if ( vmx_vcpu_pml_enabled(v) )
> +        vmx_vcpu_disable_pml(v);

Looking at this and other callers of these enable/disable functions, I
think it would be better to make those functions idempotent (i.e.
*_{en,dis}able_pml() should just return success if PML is already
enabled/disabled).  Then you don't need to check in every caller, and
there's no risk of a crash if one caller is missing the check.

Cheers,

Tim.