Re: [PATCH kernel] powerpc/mm_iommu: Allow pinning large regions

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Apr 02, 2019 at 03:31:01PM +1100, Alexey Kardashevskiy wrote:
> When called with vmas_arg==NULL, get_user_pages_longterm() allocates
> an array of nr_pages*8 which can easily get greater that the max order,
> for example, registering memory for a 256GB guest does this and fails
> in __alloc_pages_nodemask().
> 
> This adds a loop over chunks of entries to fit the max order limit.
> 
> Fixes: 678e174c4c16 ("powerpc/mm/iommu: allow migration of cma allocated pages during mm_iommu_do_alloc", 2019-03-05)
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  arch/powerpc/mm/mmu_context_iommu.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> index 36a826e23d45..e058064b013c 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -131,6 +131,7 @@ long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  	unsigned int pageshift, mem_pageshift;
>  	struct page **hpages;
>  	phys_addr_t *hpas;
> +	unsigned long entry, chunk, pinned;
>  
>  	mutex_lock(&mem_list_mutex);
>  	if (mm_iommu_find(mm, ua, entries)) {
> @@ -152,13 +153,29 @@ long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  	}
>  
>  	down_read(&mm->mmap_sem);
> -	ret = get_user_pages_longterm(ua, entries, FOLL_WRITE, hpages, NULL);
> +	chunk = (1UL << (PAGE_SHIFT + MAX_ORDER - 1)) /
> +		sizeof(struct vm_area_struct *);
> +	chunk = min(chunk, entries);

I think this is redundant with..

> +	for (entry = 0, pinned = 0; entry < entries; entry += chunk) {
> +		unsigned long n = min(entries - entry, chunk);

.. this.

But otherwise LGTM.

> +
> +		ret = get_user_pages_longterm(ua + (entry << PAGE_SHIFT), n,
> +				FOLL_WRITE, hpages + entry, NULL);
> +		if (ret == n) {
> +			pinned += n;
> +			continue;
> +		}
> +		if (ret >= 0)
> +			pinned += ret;
> +		break;
> +	}
>  	up_read(&mm->mmap_sem);
> -	if (ret != entries) {
> +	if (pinned != entries) {
>  		/* free the reference taken */
> -		for (i = 0; i < ret; i++)
> +		for (i = 0; i < pinned; i++)
>  			put_page(hpages[i]);
> -		ret = -EFAULT;
> +		if (!ret)
> +			ret = -EFAULT;
>  		goto cleanup_exit;
>  	}
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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