Subject: [PATCH v4 11/14] ARM64: KVM: fix vgic_bitmap_get_reg function for BE 64bit case

From: [email-masked] (Christoffer Dall)
Date: Sat, 14 Jun 2014 17:04:51 +0200

On Thu, Jun 12, 2014 at 09:30:10AM -0700, Victor Kamensky wrote:
> Fix vgic_bitmap_get_reg function to return 'right' word address of
> 'unsigned long' bitmap value in case of BE 64bit image.
> 
> Signed-off-by: Victor Kamensky <[email-masked]>
> ---
>  virt/kvm/arm/vgic.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 529c336..b4ffd82 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -101,14 +101,34 @@ static u32 vgic_nr_lr;
>  
>  static unsigned int vgic_maint_irq;
>  
> +/*
> + * struct vgic_bitmap contains unions that provide two views of
> + * the same data. In one case it is an array of registers of
> + * u32's, and in the other case it is a bitmap of unsigned
> + * longs.
> + *
> + * This does not work on 64-bit BE systems, because the bitmap access
> + * will store two consecutive 32-bit words with the higher-addressed
> + * register's bits at the lower index and the lower-addressed register's
> + * bits at the higher index.
> + *
> + * Therefore, swizzle the register index when accessing the 32-bit word
> + * registers to access the right register's value.
> + */
> +#if defined(CONFIG_CPU_BIG_ENDIAN) && BITS_PER_LONG == 64
> +#define REG_OFFSET_SWIZZLE	1
> +#else
> +#define REG_OFFSET_SWIZZLE	0
> +#endif
> +
>  static u32 *vgic_bitmap_get_reg(struct vgic_bitmap *x,
>  				int cpuid, u32 offset)
>  {
>  	offset >>= 2;
>  	if (!offset)
> -		return x->percpu[cpuid].reg;
> +		return x->percpu[cpuid].reg + (offset ^ REG_OFFSET_SWIZZLE);
>  	else
> -		return x->shared.reg + offset - 1;
> +		return x->shared.reg + ((offset - 1) ^ REG_OFFSET_SWIZZLE);
>  }
>  
>  static int vgic_bitmap_get_irq_val(struct vgic_bitmap *x,
> -- 
> 1.8.1.4
> 

I had wished there was a cleaner way to abstract this, but I can't think
of a cleaner solution, and restructuring the whole thing would be very
invasive.

I'm curious to hear from Marc on this one, but you can add:

Reviewed-by: Christoffer Dall <[email-masked]>

because it looks correct.

Thanks for picking up my suggestion on the commenting.

-Christoffer