Re: [PATCH v2] PC, KVM, CMA: Fix regression caused by wrong get_order() use

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> fc95ca7284bc54953165cba76c3228bd2cdb9591 claims that there is no
> functional change but this is not true as it calls get_order() (which
> takes bytes) where it should have called ilog2() and the kernel stops
> on VM_BUG_ON().
>
> This replaces get_order() with order_base_2() (round-up version of ilog2).
>
> Suggested-by: Paul Mackerras <paulus@samba.org>
> Cc: Alexander Graf <agraf@suse.de>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> ---
>
> Changes:
> v2:
> * s/ilog2/order_base_2/
> * removed cc: <stable@vger.kernel.org> as I got wrong impression that v3.16 is
> broken
>
> ---
>  arch/powerpc/kvm/book3s_hv_builtin.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
> index 329d7fd..b9615ba 100644
> --- a/arch/powerpc/kvm/book3s_hv_builtin.c
> +++ b/arch/powerpc/kvm/book3s_hv_builtin.c
> @@ -101,7 +101,7 @@ struct kvm_rma_info *kvm_alloc_rma()
>  	ri = kmalloc(sizeof(struct kvm_rma_info), GFP_KERNEL);
>  	if (!ri)
>  		return NULL;
> -	page = cma_alloc(kvm_cma, kvm_rma_pages, get_order(kvm_rma_pages));
> +	page = cma_alloc(kvm_cma, kvm_rma_pages, order_base_2(kvm_rma_pages));
>  	if (!page)
>  		goto err_out;
>  	atomic_set(&ri->use_count, 1);
> @@ -135,12 +135,12 @@ struct page *kvm_alloc_hpt(unsigned long nr_pages)
>  {
>  	unsigned long align_pages = HPT_ALIGN_PAGES;
>
> -	VM_BUG_ON(get_order(nr_pages) < KVM_CMA_CHUNK_ORDER - PAGE_SHIFT);
> +	VM_BUG_ON(order_base_2(nr_pages) < KVM_CMA_CHUNK_ORDER - PAGE_SHIFT);
>
>  	/* Old CPUs require HPT aligned on a multiple of its size */
>  	if (!cpu_has_feature(CPU_FTR_ARCH_206))
>  		align_pages = nr_pages;
> -	return cma_alloc(kvm_cma, nr_pages, get_order(align_pages));
> +	return cma_alloc(kvm_cma, nr_pages, order_base_2(align_pages));
>  }
>  EXPORT_SYMBOL_GPL(kvm_alloc_hpt);
>
> -- 
> 2.0.0