Re: [PATCH] x86: use only a single branch for upcall-pending exit path checks

[Keir Fraser <keir@xen.org>]

On 11/09/2012 12:53, "Jan Beulich" <JBeulich@suse.com> wrote:

> This utilizes the fact that the two bytes of interest are adjacent to
> one another and that the resulting 16-bit values of interest are within
> a contiguous range of numbers.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Keir Fraser <keir@xen.org>

> --- a/xen/arch/x86/x86_32/entry.S
> +++ b/xen/arch/x86/x86_32/entry.S
> @@ -219,10 +219,10 @@ test_all_events:
>          jnz  process_nmi
>  test_guest_events:
>          movl VCPU_vcpu_info(%ebx),%eax
> -        testb $0xFF,VCPUINFO_upcall_mask(%eax)
> -        jnz  restore_all_guest
> -        testb $0xFF,VCPUINFO_upcall_pending(%eax)
> -        jz   restore_all_guest
> +        movzwl VCPUINFO_upcall_pending(%eax),%eax
> +        decl %eax
> +        cmpl $0xfe,%eax
> +        ja   restore_all_guest
>  /*process_guest_events:*/
>          sti
>          leal VCPU_trap_bounce(%ebx),%edx
> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -108,10 +108,10 @@ ENTRY(compat_test_all_events)
>          jnz   compat_process_nmi
>  compat_test_guest_events:
>          movq  VCPU_vcpu_info(%rbx),%rax
> -        testb $0xFF,COMPAT_VCPUINFO_upcall_mask(%rax)
> -        jnz   compat_restore_all_guest
> -        testb $0xFF,COMPAT_VCPUINFO_upcall_pending(%rax)
> -        jz    compat_restore_all_guest
> +        movzwl COMPAT_VCPUINFO_upcall_pending(%rax),%eax
> +        decl  %eax
> +        cmpl  $0xfe,%eax
> +        ja    compat_restore_all_guest
>  /*compat_process_guest_events:*/
>          sti
>          leaq  VCPU_trap_bounce(%rbx),%rdx
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -199,8 +199,8 @@ test_all_events:
>          movl  VCPU_processor(%rbx),%eax
>          shl   $IRQSTAT_shift,%rax
>          leaq  irq_stat(%rip),%rcx
> -        testl $~0,(%rcx,%rax,1)
> -        jnz   process_softirqs
> +        cmpl  $0,(%rcx,%rax,1)
> +        jne   process_softirqs
>          testb $1,VCPU_mce_pending(%rbx)
>          jnz   process_mce
>  .Ltest_guest_nmi:
> @@ -208,10 +208,10 @@ test_all_events:
>          jnz   process_nmi
>  test_guest_events:
>          movq  VCPU_vcpu_info(%rbx),%rax
> -        testb $0xFF,VCPUINFO_upcall_mask(%rax)
> -        jnz   restore_all_guest
> -        testb $0xFF,VCPUINFO_upcall_pending(%rax)
> -        jz    restore_all_guest
> +        movzwl VCPUINFO_upcall_pending(%rax),%eax
> +        decl  %eax
> +        cmpl  $0xfe,%eax
> +        ja    restore_all_guest
>  /*process_guest_events:*/
>          sti
>          leaq  VCPU_trap_bounce(%rbx),%rdx
> 
> 
> 
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