linux-kernel - Re: [RESEND PATCH] mm/hmm: Fix initial PFN for hugetlbfs pages

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Date:   Mon, 22 Apr 2019 10:55:48 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     rcampbell@...dia.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>,
        John Hubbard <jhubbard@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RESEND PATCH] mm/hmm: Fix initial PFN for hugetlbfs pages

On Fri, Apr 19, 2019 at 04:35:36PM -0700, rcampbell@...dia.com wrote:
> From: Ralph Campbell <rcampbell@...dia.com>
> 
> The mmotm patch [1] adds hugetlbfs support for HMM but the initial
> PFN used to fill the HMM range->pfns[] array doesn't properly
> compute the starting PFN offset.
> This can be tested by running test-hugetlbfs-read from [2].
> 
> Fix the PFN offset by adjusting the page offset by the device's
> page size.
> 
> Andrew, this should probably be squashed into Jerome's patch.
> 
> [1] https://marc.info/?l=linux-mm&m=155432003506068&w=2
> ("mm/hmm: mirror hugetlbfs (snapshoting, faulting and DMA mapping)")
> [2] https://gitlab.freedesktop.org/glisse/svm-cl-tests
> 
> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>

Good catch.

Reviewed-by: Jérôme Glisse <jglisse@...hat.com>

> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Souptick Joarder <jrdr.linux@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  mm/hmm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index def451a56c3e..fcf8e4fb5770 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -868,7 +868,7 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
>  		goto unlock;
>  	}
>  
> -	pfn = pte_pfn(entry) + (start & mask);
> +	pfn = pte_pfn(entry) + ((start & mask) >> range->page_shift);
>  	for (; addr < end; addr += size, i++, pfn += pfn_inc)
>  		range->pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
>  				 cpu_flags;
> -- 
> 2.20.1
>