linux-kernel - Re: [PATCH 1/3] mm: introduce VM_MAYBE_GUARD and make visible for guard regions

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Message-ID: <6c273611-e815-4a4a-822d-f6e55cec3810@infradead.org>
Date: Wed, 29 Oct 2025 12:50:18 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, David Hildenbrand <david@...hat.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH 1/3] mm: introduce VM_MAYBE_GUARD and make visible for
 guard regions

On 10/29/25 9:50 AM, Lorenzo Stoakes wrote:

> diff --git a/mm/memory.c b/mm/memory.c
> index 4c3a7e09a159..a2c79ee43d68 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1478,6 +1478,10 @@ vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
>  	if (src_vma->anon_vma)
>  		return true;
>  
> +	/* Guard regions have momdified page tables that require copying. */

	                      modified

> +	if (src_vma->vm_flags & VM_MAYBE_GUARD)
> +		return true;
> +
>  	/*
>  	 * Don't copy ptes where a page fault will fill them correctly.  Fork
>  	 * becomes much lighter when there are big shared or private readonly
-- 
~Randy