[Skiboot] [PATCH] xive: Fix VP free block group mode false-positive parameter check

[Benjamin Herrenschmidt]

On Tue, 2017-10-10 at 02:13 +1000, Nicholas Piggin wrote:
> The check to ensure the buddy allocation idx is aligned to its
> allocation order was not taking into account the allocation split.
> This would result in opal_xive_free_vp_block failures despite
> giving the same value as returned by opal_xive_alloc_vp_block.
> 
> E.g., starting then stopping 4 KVM guests gives the following pattern
> in the host:

Ah oops :-)

>   opal_xive_alloc_vp_block(5)=0x45000020
>   opal_xive_alloc_vp_block(5)=0x45000040
>   opal_xive_alloc_vp_block(5)=0x45000060
>   opal_xive_alloc_vp_block(5)=0x45000080
>   opal_xive_free_vp_block(0x45000020)=-1
>   opal_xive_free_vp_block(0x45000040)=0
>   opal_xive_free_vp_block(0x45000060)=-1
>   opal_xive_free_vp_block(0x45000080)=0
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Acked-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

> ---
>  hw/xive.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/xive.c b/hw/xive.c
> index 26edd669..4fd8a301 100644
> --- a/hw/xive.c
> +++ b/hw/xive.c
> @@ -4463,12 +4463,14 @@ static int64_t opal_xive_free_vp_block(uint64_t vp_base)
>  		return OPAL_PARAMETER;
>  	if (order < (xive_chips_alloc_bits + 1))
>  		return OPAL_PARAMETER;
> +	if (idx & ((1 << (order - xive_chips_alloc_bits)) - 1))
> +		return OPAL_PARAMETER;
>  #else
>  	if (order < 1)
>  		return OPAL_PARAMETER;
> -#endif
>  	if (idx & ((1 << order) - 1))
>  		return OPAL_PARAMETER;
> +#endif
>  
>  	count = 1 << order;
>  	for (i = 0; i < count; i++) {