RE: [patch V3 43/44] x86/idt: Simplify alloc_intr_gate

[KY Srinivasan <kys@microsoft.com>]

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@linutronix.de]
> Sent: Sunday, August 27, 2017 11:48 PM
> To: LKML <linux-kernel@vger.kernel.org>
> Cc: Ingo Molnar <mingo@kernel.org>; Peter Anvin <hpa@zytor.com>; Peter
> Zijlstra <peterz@infradead.org>; Andy Lutomirski <luto@kernel.org>;
> Borislav Petkov <bp@alien8.de>; Steven Rostedt <rostedt@goodmis.org>;
> Juergen Gross <jgross@suse.com>; KY Srinivasan <kys@microsoft.com>;
> Stephen Hemminger <sthemmin@microsoft.com>; Boris Ostrovsky
> <boris.ostrovsky@oracle.com>
> Subject: [patch V3 43/44] x86/idt: Simplify alloc_intr_gate
> 
> The only users of alloc_intr_gate() are hypervisors, which both check the
> used_vectors bitmap whether they have allocated the gate already. Move
> that
> check into alloc_intr_gate() and simplify the users.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Juergen Gross <jgross@suse.com>
> Cc: "K. Y. Srinivasan" <kys@microsoft.com>

Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>

> Cc: Stephen Hemminger <sthemmin@microsoft.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> ---
>  arch/x86/kernel/cpu/mshyperv.c   |    9 ++-------
>  arch/x86/kernel/idt.c            |    6 +++---
>  drivers/xen/events/events_base.c |    6 ++----
>  3 files changed, 7 insertions(+), 14 deletions(-)
> 
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -59,13 +59,8 @@ void hyperv_vector_handler(struct pt_reg
>  void hv_setup_vmbus_irq(void (*handler)(void))
>  {
>  	vmbus_handler = handler;
> -	/*
> -	 * Setup the IDT for hypervisor callback. Prevent reallocation
> -	 * at module reload.
> -	 */
> -	if (!test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors))
> -		alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
> -				hyperv_callback_vector);
> +	/* Setup the IDT for hypervisor callback */
> +	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
> hyperv_callback_vector);
>  }
> 
>  void hv_remove_vmbus_irq(void)
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -354,7 +354,7 @@ void set_intr_gate(unsigned int n, const
> 
>  void alloc_intr_gate(unsigned int n, const void *addr)
>  {
> -	BUG_ON(test_bit(n, used_vectors) || n < FIRST_SYSTEM_VECTOR);
> -	set_bit(n, used_vectors);
> -	set_intr_gate(n, addr);
> +	BUG_ON(n < FIRST_SYSTEM_VECTOR);
> +	if (!test_and_set_bit(n, used_vectors))
> +		set_intr_gate(n, addr);
>  }
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -1653,10 +1653,8 @@ void xen_callback_vector(void)
>  			return;
>  		}
>  		pr_info("Xen HVM callback vector for event delivery is
> enabled\n");
> -		/* in the restore case the vector has already been allocated
> */
> -		if (!test_bit(HYPERVISOR_CALLBACK_VECTOR,
> used_vectors))
> -			alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
> -					xen_hvm_callback_vector);
> +		alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
> +				xen_hvm_callback_vector);
>  	}
>  }
>  #else
>