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Date:   Wed, 7 Dec 2022 13:31:30 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Saurabh Sengar <ssengar@linux.microsoft.com>
Cc:     ssengar@microsoft.com, yuzhao@google.com, jack@suse.cz,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        jostarks@microsoft.com
Subject: Re: [PATCH v2] mm/gup: fix gup_pud_range() for dax
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On Tue,  6 Dec 2022 22:00:53 -0800 Saurabh Sengar <ssengar@linux.microsoft.com> wrote:

> From: John Starks <jostarks@microsoft.com>
> 
> For dax pud, pud_huge() returns true on x86. So the function works as long
> as hugetlb is configured. However, dax doesn't depend on hugetlb.
> Commit 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") fixed
> devmap-backed huge PMDs, but missed devmap-backed huge PUDs. Fix this as
> well.
> 
> This fixes the below kernel panic:
> 
> ...
>
> Fixes: 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax")

Feb 2019.

> Signed-off-by: John Starks <jostarks@microsoft.com>
> Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> ---
>  mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index c2c2c6d..e776540 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2765,7 +2765,7 @@ static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned lo
>  		next = pud_addr_end(addr, end);
>  		if (unlikely(!pud_present(pud)))
>  			return 0;
> -		if (unlikely(pud_huge(pud))) {
> +		if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
>  			if (!gup_huge_pud(pud, pudp, addr, next, flags,
>  					  pages, nr))
>  				return 0;

I assume this should be backported into -stable kernels?