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

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

[Alexey Kardashevskiy]

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 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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 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..bfe9f01 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, ilog2(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(ilog2(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, ilog2(align_pages));
 }
 EXPORT_SYMBOL_GPL(kvm_alloc_hpt);
 
-- 
2.0.0

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

[Aneesh Kumar K.V]

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 ilog2().

Should we round it up ? ie, ilog2(kvm_rma_pages - 1) + 1 ?

>
> 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>
> Cc: <stable@vger.kernel.org>

Why stable ? We merged it this merge window.

> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  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..bfe9f01 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, ilog2(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(ilog2(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, ilog2(align_pages));
>  }
>  EXPORT_SYMBOL_GPL(kvm_alloc_hpt);
>
> -- 
> 2.0.0