From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Usama Arif <usama.arif@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
apopple@nvidia.com, byungchul@sk.com, david@kernel.org,
gourry@gourry.net, jannh@google.com, joshua.hahnjy@gmail.com,
liam@infradead.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org,
matthew.brost@intel.com, mhocko@suse.com, pfalcato@suse.de,
rppt@kernel.org, surenb@google.com, vbabka@kernel.org,
ying.huang@linux.alibaba.com, ziy@nvidia.com, kas@kernel.org,
hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev,
kernel-team@meta.com, Nico Pache <nico.pache@linux.dev>,
ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org,
lance.yang@linux.dev
Cc: stable@vger.kernel.org
Subject: Re: [PATCH 2/3] fs/proc/task_mmu: don't read young/dirty from a non-present PMD in smaps
Date: Thu, 12 Nov 2026 15:40:11 +0800 [thread overview]
Message-ID: <c92a3132-da7d-46f7-bd06-6beffa3d2e34@linux.alibaba.com> (raw)
In-Reply-To: <20261111113904.650722-3-usama.arif@linux.dev>
On 11/11/26 7:38 PM, Usama Arif wrote:
> smaps_pmd_entry() passes pmd_young(*pmd) and pmd_dirty(*pmd) to
> smaps_account() for every PMD, including migration and device-private
> entries, where those bits hold part of the swap offset rather than
> accessed/dirty state. smaps_pte_entry() only reads them when the entry
> is present.
>
> On x86_64 the offset is stored inverted across bits 9-58, which overlap
> _PAGE_SAVED_DIRTY, so pmd_dirty() returns garbage: a clean 2MB
> device-private mapping is accounted as 2048 kB dirty, and lazyfree
> accounting is suppressed. pgtable_64.h also warns that the hardware can
> set the accessed and dirty bits on non-present entries by mistake.
>
> Only read the bits when the PMD is present.
>
> Fixes: c94b6923fa0a ("/proc/PID/smaps: Add PMD migration entry parsing")
> Cc: stable@vger.kernel.org
> Signed-off-by: Usama Arif <usama.arif@linux.dev>
> ---
Make sense to me.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
next prev parent reply other threads:[~2026-11-12 7:40 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-11 11:38 [PATCH 0/3] mm: fixes for THP migration, swap-in and device-private smaps Usama Arif
2026-11-11 11:38 ` [PATCH 1/3] mm: don't PTE-batch a swap-in over a hardware-poisoned subpage Usama Arif
2026-11-11 13:18 ` Lorenzo Stoakes (ARM)
2026-11-11 18:39 ` Usama Arif
2026-11-12 11:52 ` Lorenzo Stoakes (ARM)
2026-11-12 8:56 ` David Hildenbrand (Arm)
2026-11-12 11:54 ` Lorenzo Stoakes (ARM)
2026-11-11 18:50 ` Zi Yan
2026-11-11 11:38 ` [PATCH 2/3] fs/proc/task_mmu: don't read young/dirty from a non-present PMD in smaps Usama Arif
2026-11-11 13:27 ` Lorenzo Stoakes (ARM)
2026-11-12 7:40 ` Baolin Wang [this message]
2026-11-12 8:57 ` David Hildenbrand (Arm)
2026-11-12 15:44 ` Zi Yan
2026-11-11 11:38 ` [PATCH 3/3] fs/proc/task_mmu: account device-private PMDs as present " Usama Arif
2026-11-11 13:30 ` Lorenzo Stoakes (ARM)
2026-11-12 9:00 ` David Hildenbrand (Arm)
2026-11-12 15:46 ` Zi Yan
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