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Subject: Re: [PATCH 08/13] mm: remove the mask variable in
 hmm_vma_walk_hugetlb_entry
To:     Christoph Hellwig <hch@lst.de>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Ben Skeggs <bskeggs@redhat.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>
CC:     <linux-mm@kvack.org>, <nouveau@lists.freedesktop.org>,
        <dri-devel@lists.freedesktop.org>, <amd-gfx@lists.freedesktop.org>,
        <linux-kernel@vger.kernel.org>
References: <20190730055203.28467-1-hch@lst.de>
 <20190730055203.28467-9-hch@lst.de>
From:   Ralph Campbell <rcampbell@nvidia.com>
Message-ID: <5f8e6310-5e97-3e57-bfbf-5eef553b4d91@nvidia.com>
Date:   Tue, 30 Jul 2019 18:01:11 -0700
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On 7/29/19 10:51 PM, Christoph Hellwig wrote:
> The pagewalk code already passes the value as the hmask parameter.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   mm/hmm.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index f26d6abc4ed2..88b77a4a6a1e 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -771,19 +771,16 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
>   				      struct mm_walk *walk)
>   {
>   #ifdef CONFIG_HUGETLB_PAGE
> -	unsigned long addr = start, i, pfn, mask;
> +	unsigned long addr = start, i, pfn;
>   	struct hmm_vma_walk *hmm_vma_walk = walk->private;
>   	struct hmm_range *range = hmm_vma_walk->range;
>   	struct vm_area_struct *vma = walk->vma;
> -	struct hstate *h = hstate_vma(vma);
>   	uint64_t orig_pfn, cpu_flags;
>   	bool fault, write_fault;
>   	spinlock_t *ptl;
>   	pte_t entry;
>   	int ret = 0;
>   
> -	mask = huge_page_size(h) - 1;
> -
>   	ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
>   	entry = huge_ptep_get(pte);
>   
> @@ -799,7 +796,7 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
>   		goto unlock;
>   	}
>   
> -	pfn = pte_pfn(entry) + ((start & mask) >> PAGE_SHIFT);
> +	pfn = pte_pfn(entry) + ((start & hmask) >> PAGE_SHIFT);

This needs to be "~hmask" so that the upper bits of the start address
are not added to the pfn. It's the middle bits of the address that
offset into the huge page that are needed.

>   	for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
>   		range->pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
>   				 cpu_flags;
>