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

From: Aneesh Kumar K.V
Date: Wed Aug 13 2014 - 07:56:38 EST


Alexey Kardashevskiy <aik@xxxxxxxxx> 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@xxxxxxxxx>
> Cc: Alexander Graf <agraf@xxxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>

Why stable ? We merged it this merge window.

> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> ---
> 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

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