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Message-ID: <CAMgjq7AP383YfU3L5ZxJ9U3x-vRPnEkEUtmnPdXD29HiNC8OrA@mail.gmail.com>
Date: Sun, 9 Nov 2025 20:49:02 +0800
From: Kairui Song <ryncsn@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>, David Hildenbrand <david@...hat.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>, Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>, Peter Xu <peterx@...hat.com>,
Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
Arnd Bergmann <arnd@...db.de>, Zi Yan <ziy@...dia.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
Lance Yang <lance.yang@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
Oscar Salvador <osalvador@...e.de>, Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
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Ying Huang <ying.huang@...ux.alibaba.com>, Alistair Popple <apopple@...dia.com>,
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Wei Xu <weixugc@...gle.com>, Kemeng Shi <shikemeng@...weicloud.com>,
Nhat Pham <nphamcs@...il.com>, Baoquan He <bhe@...hat.com>, Chris Li <chrisl@...nel.org>,
SeongJae Park <sj@...nel.org>, Matthew Wilcox <willy@...radead.org>, Jason Gunthorpe <jgg@...pe.ca>,
Leon Romanovsky <leon@...nel.org>, Xu Xin <xu.xin16@....com.cn>,
Chengming Zhou <chengming.zhou@...ux.dev>, Jann Horn <jannh@...gle.com>,
Miaohe Lin <linmiaohe@...wei.com>, Naoya Horiguchi <nao.horiguchi@...il.com>,
Pedro Falcato <pfalcato@...e.de>, Pasha Tatashin <pasha.tatashin@...een.com>,
Rik van Riel <riel@...riel.com>, Harry Yoo <harry.yoo@...cle.com>, Hugh Dickins <hughd@...gle.com>,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org, linux-s390@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-arch@...r.kernel.org,
damon@...ts.linux.dev
Subject: Re: [PATCH v2 04/16] mm: eliminate is_swap_pte() when
softleaf_from_pte() suffices
On Sun, Nov 9, 2025 at 2:16 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> In cases where we can simply utilise the fact that softleaf_from_pte()
> treats present entries as if they were none entries and thus eliminate
> spurious uses of is_swap_pte(), do so.
>
> No functional change intended.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
> mm/internal.h | 7 +++----
> mm/madvise.c | 8 +++-----
> mm/swap_state.c | 12 ++++++------
> mm/swapfile.c | 9 ++++-----
> 4 files changed, 16 insertions(+), 20 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 9465129367a4..f0c7461bb02c 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -15,7 +15,7 @@
> #include <linux/pagewalk.h>
> #include <linux/rmap.h>
> #include <linux/swap.h>
> -#include <linux/swapops.h>
> +#include <linux/leafops.h>
> #include <linux/swap_cgroup.h>
> #include <linux/tracepoint-defs.h>
>
> @@ -380,13 +380,12 @@ static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte)
> {
> pte_t expected_pte = pte_next_swp_offset(pte);
> const pte_t *end_ptep = start_ptep + max_nr;
> - swp_entry_t entry = pte_to_swp_entry(pte);
> + const softleaf_t entry = softleaf_from_pte(pte);
> pte_t *ptep = start_ptep + 1;
> unsigned short cgroup_id;
>
> VM_WARN_ON(max_nr < 1);
> - VM_WARN_ON(!is_swap_pte(pte));
> - VM_WARN_ON(non_swap_entry(entry));
> + VM_WARN_ON(!softleaf_is_swap(entry));
>
> cgroup_id = lookup_swap_cgroup_id(entry);
> while (ptep < end_ptep) {
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 2d5ad3cb37bb..58d82495b6c6 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -195,7 +195,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
>
> for (addr = start; addr < end; addr += PAGE_SIZE) {
> pte_t pte;
> - swp_entry_t entry;
> + softleaf_t entry;
> struct folio *folio;
>
> if (!ptep++) {
> @@ -205,10 +205,8 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
> }
>
> pte = ptep_get(ptep);
> - if (!is_swap_pte(pte))
> - continue;
> - entry = pte_to_swp_entry(pte);
> - if (unlikely(non_swap_entry(entry)))
> + entry = softleaf_from_pte(pte);
> + if (unlikely(!softleaf_is_swap(entry)))
> continue;
>
> pte_unmap_unlock(ptep, ptl);
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index d20d238109f9..8881a79f200c 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -12,7 +12,7 @@
> #include <linux/kernel_stat.h>
> #include <linux/mempolicy.h>
> #include <linux/swap.h>
> -#include <linux/swapops.h>
> +#include <linux/leafops.h>
> #include <linux/init.h>
> #include <linux/pagemap.h>
> #include <linux/pagevec.h>
> @@ -732,7 +732,6 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
> pte_t *pte = NULL, pentry;
> int win;
> unsigned long start, end, addr;
> - swp_entry_t entry;
> pgoff_t ilx;
> bool page_allocated;
>
> @@ -744,16 +743,17 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
>
> blk_start_plug(&plug);
> for (addr = start; addr < end; ilx++, addr += PAGE_SIZE) {
> + softleaf_t entry;
> +
> if (!pte++) {
> pte = pte_offset_map(vmf->pmd, addr);
> if (!pte)
> break;
> }
> pentry = ptep_get_lockless(pte);
> - if (!is_swap_pte(pentry))
> - continue;
> - entry = pte_to_swp_entry(pentry);
> - if (unlikely(non_swap_entry(entry)))
> + entry = softleaf_from_pte(pentry);
> +
> + if (!softleaf_is_swap(entry))
Hi Lorenzo,
This part isn't right, is_swap_pte excludes present PTE and non PTE,
but softleaf_from_pte returns a invalid swap entry from a non PTE.
This may lead to a kernel panic as the invalid swap value will be
0x3ffffffffffff on x86_64 (pte_to_swp_entry(0)), the offset value will
cause out of border access.
We might need something like this on top of patch 2:
diff --git a/include/linux/leafops.h b/include/linux/leafops.h
index 1376589d94b0..49de62f96835 100644
--- a/include/linux/leafops.h
+++ b/include/linux/leafops.h
@@ -54,7 +54,7 @@ static inline softleaf_t softleaf_mk_none(void)
*/
static inline softleaf_t softleaf_from_pte(pte_t pte)
{
- if (pte_present(pte))
+ if (pte_present(pte) || pte_none(pte))
return softleaf_mk_none();
/* Temporary until swp_entry_t eliminated. */
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