[PATCH STABLE v4.19.y] mm/migrate: set swap entry values of THP tail pages properly.

[PATCH STABLE v4.19.y] mm/migrate: set swap entry values of THP tail pages properly.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

The tail pages in a THP can have swap entry information stored in their
private field. When migrating to a new page, all tail pages of the new
page need to update ->private to avoid future data corruption.

This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory:
work on folio->swap instead of page->private when splitting folio"),
subpages of a swapcached THP no longer requires the maintenance.

Adding THPs to the swapcache was introduced in commit
38d8b4e6bdc87 ("mm, THP, swap: delay splitting THP during swap out"),
where each subpage of a THP added to the swapcache had its own swapcache
entry and required the ->private field to point to the correct swapcache
entry. Later, when THP migration functionality was implemented in commit
616b8371539a6 ("mm: thp: enable thp migration in generic path"),
it initially did not handle the subpages of swapcached THPs, failing to
update their ->private fields or replace the subpage pointers in the
swapcache. Subsequently, commit e71769ae5260 ("mm: enable thp migration
for shmem thp") addressed the swapcache update aspect. This patch fixes
the update of subpage ->private fields.

Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 mm/migrate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 171573613c39..893ea04498f7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -514,8 +514,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
 	if (PageSwapBacked(page)) {
 		__SetPageSwapBacked(newpage);
 		if (PageSwapCache(page)) {
+			int i;
+
 			SetPageSwapCache(newpage);
-			set_page_private(newpage, page_private(page));
+			for (i = 0; i < (1 << compound_order(page)); i++)
+				set_page_private(newpage + i,
+						 page_private(page + i));
 		}
 	} else {
 		VM_BUG_ON_PAGE(PageSwapCache(page), page);
-- 
2.43.0

Re: [PATCH STABLE v4.19.y] mm/migrate: set swap entry values of THP tail pages properly.

[Greg KH]

On Wed, Mar 06, 2024 at 10:50:52AM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> The tail pages in a THP can have swap entry information stored in their
> private field. When migrating to a new page, all tail pages of the new
> page need to update ->private to avoid future data corruption.
> 
> This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory:
> work on folio->swap instead of page->private when splitting folio"),
> subpages of a swapcached THP no longer requires the maintenance.
> 
> Adding THPs to the swapcache was introduced in commit
> 38d8b4e6bdc87 ("mm, THP, swap: delay splitting THP during swap out"),
> where each subpage of a THP added to the swapcache had its own swapcache
> entry and required the ->private field to point to the correct swapcache
> entry. Later, when THP migration functionality was implemented in commit
> 616b8371539a6 ("mm: thp: enable thp migration in generic path"),
> it initially did not handle the subpages of swapcached THPs, failing to
> update their ->private fields or replace the subpage pointers in the
> swapcache. Subsequently, commit e71769ae5260 ("mm: enable thp migration
> for shmem thp") addressed the swapcache update aspect. This patch fixes
> the update of subpage ->private fields.
> 
> Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/migrate.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 171573613c39..893ea04498f7 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -514,8 +514,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
>  	if (PageSwapBacked(page)) {
>  		__SetPageSwapBacked(newpage);
>  		if (PageSwapCache(page)) {
> +			int i;
> +
>  			SetPageSwapCache(newpage);
> -			set_page_private(newpage, page_private(page));
> +			for (i = 0; i < (1 << compound_order(page)); i++)
> +				set_page_private(newpage + i,
> +						 page_private(page + i));
>  		}
>  	} else {
>  		VM_BUG_ON_PAGE(PageSwapCache(page), page);
> -- 
> 2.43.0
> 
> 

All now queued up, thanks.

greg k-h

Patch "mm/migrate: set swap entry values of THP tail pages properly." has been added to the 4.19-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    mm/migrate: set swap entry values of THP tail pages properly.

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-migrate-set-swap-entry-values-of-thp-tail-pages-properly.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-26997-greg=kroah.com@vger.kernel.org Wed Mar  6 16:51:02 2024
From: Zi Yan <zi.yan@sent.com>
Date: Wed,  6 Mar 2024 10:50:52 -0500
Subject: mm/migrate: set swap entry values of THP tail pages properly.
To: gregkh@linuxfoundation.org, stable@vger.kernel.org
Cc: Zi Yan <ziy@nvidia.com>, linux-mm@kvack.org, Charan Teja Kalla <quic_charante@quicinc.com>, "Matthew Wilcox (Oracle)" <willy@infradead.org>, David Hildenbrand <david@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Huang Ying <ying.huang@intel.com>, Naoya Horiguchi <naoya.horiguchi@linux.dev>
Message-ID: <20240306155052.118007-1-zi.yan@sent.com>

From: Zi Yan <ziy@nvidia.com>

The tail pages in a THP can have swap entry information stored in their
private field. When migrating to a new page, all tail pages of the new
page need to update ->private to avoid future data corruption.

This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory:
work on folio->swap instead of page->private when splitting folio"),
subpages of a swapcached THP no longer requires the maintenance.

Adding THPs to the swapcache was introduced in commit
38d8b4e6bdc87 ("mm, THP, swap: delay splitting THP during swap out"),
where each subpage of a THP added to the swapcache had its own swapcache
entry and required the ->private field to point to the correct swapcache
entry. Later, when THP migration functionality was implemented in commit
616b8371539a6 ("mm: thp: enable thp migration in generic path"),
it initially did not handle the subpages of swapcached THPs, failing to
update their ->private fields or replace the subpage pointers in the
swapcache. Subsequently, commit e71769ae5260 ("mm: enable thp migration
for shmem thp") addressed the swapcache update aspect. This patch fixes
the update of subpage ->private fields.

Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/migrate.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -514,8 +514,12 @@ int migrate_page_move_mapping(struct add
 	if (PageSwapBacked(page)) {
 		__SetPageSwapBacked(newpage);
 		if (PageSwapCache(page)) {
+			int i;
+
 			SetPageSwapCache(newpage);
-			set_page_private(newpage, page_private(page));
+			for (i = 0; i < (1 << compound_order(page)); i++)
+				set_page_private(newpage + i,
+						 page_private(page + i));
 		}
 	} else {
 		VM_BUG_ON_PAGE(PageSwapCache(page), page);


Patches currently in stable-queue which might be from kroah.com@vger.kernel.org are

queue-4.19/loop-factor-out-configuring-loop-from-status.patch
queue-4.19/loop-call-loop_config_discard-only-after-new-config-is-applied.patch
queue-4.19/loop-refactor-loop_set_status-size-calculation.patch
queue-4.19/loop-factor-out-setting-loop-device-size.patch
queue-4.19/loop-check-for-overflow-while-configuring-loop.patch
queue-4.19/loop-properly-observe-rotational-flag-of-underlying-device.patch
queue-4.19/loop-remove-sector_t-truncation-checks.patch
queue-4.19/revert-loop-check-for-overflow-while-configuring-loop.patch
queue-4.19/loop-loop_set_status_from_info-check-before-assignment.patch
queue-4.19/mm-migrate-set-swap-entry-values-of-thp-tail-pages-properly.patch

[PATCH STABLE v4.19.y] mm/migrate: set swap entry values of THP tail pages properly.

[Zi Yan]

From: Zi Yan <ziy@nvidia.com>

The tail pages in a THP can have swap entry information stored in their
private field. When migrating to a new page, all tail pages of the new
page need to update ->private to avoid future data corruption.

Corresponding swapcache entries need to be updated as well.
e71769ae5260 ("mm: enable thp migration for shmem thp") fixed it already.

Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/migrate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 171573613c39..893ea04498f7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -514,8 +514,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
 	if (PageSwapBacked(page)) {
 		__SetPageSwapBacked(newpage);
 		if (PageSwapCache(page)) {
+			int i;
+
 			SetPageSwapCache(newpage);
-			set_page_private(newpage, page_private(page));
+			for (i = 0; i < (1 << compound_order(page)); i++)
+				set_page_private(newpage + i,
+						 page_private(page + i));
 		}
 	} else {
 		VM_BUG_ON_PAGE(PageSwapCache(page), page);
-- 
2.43.0

Re: [PATCH STABLE v4.19.y] mm/migrate: set swap entry values of THP tail pages properly.

[David Hildenbrand]

On 05.03.24 17:32, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> The tail pages in a THP can have swap entry information stored in their
> private field. When migrating to a new page, all tail pages of the new
> page need to update ->private to avoid future data corruption.
> 
> Corresponding swapcache entries need to be updated as well.
> e71769ae5260 ("mm: enable thp migration for shmem thp") fixed it already.
> 
> Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>   mm/migrate.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 171573613c39..893ea04498f7 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -514,8 +514,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
>   	if (PageSwapBacked(page)) {
>   		__SetPageSwapBacked(newpage);
>   		if (PageSwapCache(page)) {
> +			int i;
> +
>   			SetPageSwapCache(newpage);
> -			set_page_private(newpage, page_private(page));
> +			for (i = 0; i < (1 << compound_order(page)); i++)
> +				set_page_private(newpage + i,
> +						 page_private(page + i));
>   		}
>   	} else {
>   		VM_BUG_ON_PAGE(PageSwapCache(page), page);

Thanks for taking care of all of these!

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

-- 
Cheers,

David / dhildenb