[PATCH] ARM: KVM: avoid add/sub on vcpu pointer

[Christoffer Dall]

On Tue, Jan 15, 2013 at 6:20 AM, Marc Zyngier <marc.zyngier at arm.com> wrote:
> Doing arithmetic on the vcpu pointer can be avoided by using
> another register as a base. Saves a few instructions on the
> switch path.
>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm/kvm/interrupts_head.S | 32 ++++++++++++++------------------
>  1 file changed, 14 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
> index 0e423be..d2442f9 100644
> --- a/arch/arm/kvm/interrupts_head.S
> +++ b/arch/arm/kvm/interrupts_head.S
> @@ -264,11 +264,10 @@ vcpu      .req    r0              @ vcpu pointer always in r0
>         str     r3, [vcpu, #CP15_OFFSET(c1_CPACR)]
>         str     r4, [vcpu, #CP15_OFFSET(c2_TTBCR)]
>         str     r5, [vcpu, #CP15_OFFSET(c3_DACR)]
> -       add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR0)
> -       strd    r6, r7, [vcpu]
> -       add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1) - CP15_OFFSET(c2_TTBR0)
> -       strd    r8, r9, [vcpu]
> -       sub     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1)
> +       add     r2, vcpu, #CP15_OFFSET(c2_TTBR0)
> +       strd    r6, r7, [r2]
> +       add     r2, vcpu, #CP15_OFFSET(c2_TTBR1)
> +       strd    r8, r9, [r2]
>         str     r10, [vcpu, #CP15_OFFSET(c10_PRRR)]
>         str     r11, [vcpu, #CP15_OFFSET(c10_NMRR)]
>         str     r12, [vcpu, #CP15_OFFSET(c0_CSSELR)]
> @@ -362,11 +361,10 @@ vcpu      .req    r0              @ vcpu pointer always in r0
>         ldr     r3, [vcpu, #CP15_OFFSET(c1_CPACR)]
>         ldr     r4, [vcpu, #CP15_OFFSET(c2_TTBCR)]
>         ldr     r5, [vcpu, #CP15_OFFSET(c3_DACR)]
> -       add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR0)
> -       ldrd    r6, r7, [vcpu]
> -       add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1) - CP15_OFFSET(c2_TTBR0)
> -       ldrd    r8, r9, [vcpu]
> -       sub     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1)
> +       add     r12, vcpu, #CP15_OFFSET(c2_TTBR0)
> +       ldrd    r6, r7, [r12]
> +       add     r12, vcpu, #CP15_OFFSET(c2_TTBR1)
> +       ldrd    r8, r9, [r12]
>         ldr     r10, [vcpu, #CP15_OFFSET(c10_PRRR)]
>         ldr     r11, [vcpu, #CP15_OFFSET(c10_NMRR)]
>         ldr     r12, [vcpu, #CP15_OFFSET(c0_CSSELR)]
> @@ -479,7 +477,7 @@ vcpu        .req    r0              @ vcpu pointer always in r0
>   * for the host.
>   *
>   * Assumes vcpu pointer in vcpu reg
> - * Clobbers r2-r4
> + * Clobbers r2-r5
>   */
>  .macro save_timer_state
>  #ifdef CONFIG_KVM_ARM_TIMER
> @@ -496,9 +494,8 @@ vcpu        .req    r0              @ vcpu pointer always in r0
>
>         mrrc    p15, 3, r2, r3, c14     @ CNTV_CVAL
>         ldr     r4, =VCPU_TIMER_CNTV_CVAL
> -       add     vcpu, vcpu, r4
> -       strd    r2, r3, [vcpu]
> -       sub     vcpu, vcpu, r4
> +       add     r5, vcpu, r4
> +       strd    r2, r3, [r5]
>
>  1:
>  #endif
> @@ -513,7 +510,7 @@ vcpu        .req    r0              @ vcpu pointer always in r0
>   * for the host.
>   *
>   * Assumes vcpu pointer in vcpu reg
> - * Clobbers r2-r4
> + * Clobbers r2-r5
>   */
>  .macro restore_timer_state
>         @ Disallow physical timer access for the guest
> @@ -534,9 +531,8 @@ vcpu        .req    r0              @ vcpu pointer always in r0
>         mcrr    p15, 4, r2, r3, c14     @ CNTVOFF
>
>         ldr     r4, =VCPU_TIMER_CNTV_CVAL
> -       add     vcpu, vcpu, r4
> -       ldrd    r2, r3, [vcpu]
> -       sub     vcpu, vcpu, r4
> +       add     r5, vcpu, r4
> +       ldrd    r2, r3, [r5]
>         mcrr    p15, 3, r2, r3, c14     @ CNTV_CVAL
>         isb
>
> --
> 1.8.1
>
much nicer, thanks.

-Christoffer