Re: [Xen-devel] [PATCH RFC v12 03/21] Remove an unnecessary assert from vmx_update_debug_state

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 13 Sep 2013 17:25:03 +0100
George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:

> As far as I can tell, there's nothing here that requires v to be
> current.  vmx_update_exception_bitmap() is updated in other situations
> where v!=current.
> 
> Removing this allows the PVH code to call this during vmcs
> construction in a later patch, making the code more robust by removing
> duplicate code.
> 
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> CC: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> CC: Jan Beulich <jan.beulich@xxxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> CC: Keir Fraser <keir@xxxxxxx>
> ---
>  xen/arch/x86/hvm/vmx/vmx.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 8ed7026..f02e47a 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1041,8 +1041,6 @@ void vmx_update_debug_state(struct vcpu *v)
>  {
>      unsigned long mask;
>  
> -    ASSERT(v == current);
> -
>      mask = 1u << TRAP_int3;
>      if ( !cpu_has_monitor_trap_flag )
>          mask |= 1u << TRAP_debug;


vmx_update_exception_bitmap() writes EXCEPTION_BITMAP of current vmcs,
ie of current vcpu. If v != current, you'd be writing the bitmap of
wrong vcpu. If the assertion is removed, then the function would need
to vmx enter... 

mukesh


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