linux-kernel - Re: [PATCH 02/10] mm/hmm: do not erase snapshot when a range is invalidated

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Message-ID: <ca5e182d-6b99-0e5d-91ab-175ddc6acd45@nvidia.com>
Date:   Wed, 20 Feb 2019 15:58:40 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     <jglisse@...hat.com>, <linux-mm@...ck.org>
CC:     <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH 02/10] mm/hmm: do not erase snapshot when a range is
 invalidated

On 1/29/19 8:54 AM, jglisse@...hat.com wrote:
> From: Jérôme Glisse <jglisse@...hat.com>
> 
> Users of HMM might be using the snapshot information to do
> preparatory step like dma mapping pages to a device before
> checking for invalidation through hmm_vma_range_done() so
> do not erase that information and assume users will do the
> right thing.
> 
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> ---
>   mm/hmm.c | 6 ------
>   1 file changed, 6 deletions(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index b9f384ea15e9..74d69812d6be 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -170,16 +170,10 @@ static int hmm_invalidate_range(struct hmm *hmm, bool device,
>   
>   	spin_lock(&hmm->lock);
>   	list_for_each_entry(range, &hmm->ranges, list) {
> -		unsigned long addr, idx, npages;
> -
>   		if (update->end < range->start || update->start >= range->end)
>   			continue;
>   
>   		range->valid = false;
> -		addr = max(update->start, range->start);
> -		idx = (addr - range->start) >> PAGE_SHIFT;
> -		npages = (min(range->end, update->end) - addr) >> PAGE_SHIFT;
> -		memset(&range->pfns[idx], 0, sizeof(*range->pfns) * npages);
>   	}
>   	spin_unlock(&hmm->lock);
>   
> 

Seems harmless to me. I really cannot see how this could cause a problem,
so you can add:

	Reviewed-by: John Hubbard <jhubbard@...dia.com>

thanks,
-- 
John Hubbard
NVIDIA