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Sun, 10 May 2026 23:57:12 -0700 (PDT) Received: from intel.company.local ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-367d684009esm6708662a91.11.2026.05.10.23.57.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 10 May 2026 23:57:12 -0700 (PDT) From: Wandun Chen X-Google-Original-From: Wandun Chen To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev Subject: [PATCH v2] mm/khugepaged: avoid underflow in madvise_collapse for sub-PMD MADV_COLLAPSE Date: Mon, 11 May 2026 14:57:01 +0800 Message-ID: <20260511065701.799006-1-chenwandun@lixiang.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Chen Wandun madvise_collapse() computes the THP-aligned window: hstart = ALIGN(start, HPAGE_PMD_SIZE); /* round up */ hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); /* round down */ The following case will cause hstart > hend, and result in underflow in the return statement, avoid it by returning -EINVAL early when hstart > hend. madvise(PMD-aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); In addition, kmalloc_obj(), mmgrab() and lru_add_drain_all() are unnecessary when hstart == hend, so skip these operations by returning early too. Signed-off-by: Chen Wandun --- v1 --> v2: - Rebase and resolve code conflict. - Return -EINVAL when hstart > hend, suggested by Lorenzo. - Drop Fixes tag, suggested by David and Lorenzo. - Updated commit message to be more explicit, suggested by Lorenzo. --- mm/khugepaged.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 28a843f30b32..36baab17f098 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2837,6 +2837,15 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER)) return -EINVAL; + hstart = ALIGN(start, HPAGE_PMD_SIZE); + hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); + + if (hstart > hend) + return -EINVAL; + + if (hstart == hend) + return 0; + cc = kmalloc_obj(*cc); if (!cc) return -ENOMEM; @@ -2846,9 +2855,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, mmgrab(mm); lru_add_drain_all(); - hstart = ALIGN(start, HPAGE_PMD_SIZE); - hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); - for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { enum scan_result result = SCAN_FAIL; -- 2.43.0