linux-kernel - Re: [PATCH 1/2] fs/proc: extend the PAGEMAP

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Message-ID: <43657a07-617b-43fe-b0b0-689f2392fc63@redhat.com>
Date: Fri, 21 Mar 2025 11:49:31 +0100
From: David Hildenbrand <david@...hat.com>
To: Andrei Vagin <avagin@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
 Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
 Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH 1/2] fs/proc: extend the PAGEMAP_SCAN ioctl to report
 guard regions

On 20.03.25 07:39, Andrei Vagin wrote:
> From: Andrei Vagin <avagin@...il.com>
> 
> Introduce the PAGE_IS_GUARD flag in the PAGEMAP_SCAN ioctl to expose
> information about guard regions. This allows userspace tools, such as
> CRIU, to detect and handle guard regions.
> 
> Signed-off-by: Andrei Vagin <avagin@...il.com>
> ---
>   Documentation/admin-guide/mm/pagemap.rst | 1 +
>   fs/proc/task_mmu.c                       | 8 ++++++--
>   include/uapi/linux/fs.h                  | 1 +
>   3 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
> index a297e824f990..7997b67ffc97 100644
> --- a/Documentation/admin-guide/mm/pagemap.rst
> +++ b/Documentation/admin-guide/mm/pagemap.rst
> @@ -234,6 +234,7 @@ Following flags about pages are currently supported:
>   - ``PAGE_IS_PFNZERO`` - Page has zero PFN
>   - ``PAGE_IS_HUGE`` - Page is PMD-mapped THP or Hugetlb backed
>   - ``PAGE_IS_SOFT_DIRTY`` - Page is soft-dirty
> +- ``PAGE_IS_GUARD`` - Page is a guard region
>   
>   The ``struct pm_scan_arg`` is used as the argument of the IOCTL.
>   
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index c17615e21a5d..698d660bfee4 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -2067,7 +2067,8 @@ static int pagemap_release(struct inode *inode, struct file *file)
>   #define PM_SCAN_CATEGORIES	(PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN |	\
>   				 PAGE_IS_FILE |	PAGE_IS_PRESENT |	\
>   				 PAGE_IS_SWAPPED | PAGE_IS_PFNZERO |	\
> -				 PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY)
> +				 PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY |	\
> +				 PAGE_IS_GUARD)
>   #define PM_SCAN_FLAGS		(PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
>   
>   struct pagemap_scan_private {
> @@ -2108,8 +2109,11 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
>   		if (!pte_swp_uffd_wp_any(pte))
>   			categories |= PAGE_IS_WRITTEN;
>   
> +		swp = pte_to_swp_entry(pte);
> +		if (is_guard_swp_entry(swp))
> +			categories |= PAGE_IS_GUARD;
> +
>   		if (p->masks_of_interest & PAGE_IS_FILE) {

could be an else if?

if (is_guard_swp_entry(swp)) {
	categories |= PAGE_IS_GUARD;
} else if (p->masks_of_interest & PAGE_IS_FILE) {
...


Acked-by: David Hildenbrand <david@...hat.com>


-- 
Cheers,

David / dhildenb