linux-kernel - Re: [PATCH] mm/hugetlb: Move vmf_anon_prepare upfront in hugetlb

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Message-ID: <ZlSQnLvqIILiayiW@localhost.localdomain>
Date: Mon, 27 May 2024 15:54:36 +0200
From: Oscar Salvador <osalvador@...e.de>
To: David Hildenbrand <dhildenb@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Muchun Song <muchun.song@...ux.dev>,
	Vishal Moola <vishal.moola@...il.com>
Subject: Re: [PATCH] mm/hugetlb: Move vmf_anon_prepare upfront in hugetlb_wp

On Mon, May 27, 2024 at 03:17:01PM +0200, David Hildenbrand wrote:
> gup_must_unshare() without a VMA is only used for GUP-fast. Before
> triggering a page fault we always fallback to GUP-slow first, where we have
> a VMA.

I see, thanks for explaining!

> IMHO we better not make assumptions that hugetlb_wp() will always already
> have an anon VMA.

Fine by me, I just wanted to have the picture more clear, because I could not
see how we could end up in such situation, but better be safe and than sorry.

@Andrew: This fix is to avoid an issue like [1], but for hugetlb_wp().

[1] https://lore.kernel.org/linux-mm/000000000000daf1e10615e64dcb@google.com/T/
 

-- 
Oscar Salvador
SUSE Labs