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[80.230.48.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e65607127sm10239565e9.1.2026.05.07.15.22.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 May 2026 15:22:30 -0700 (PDT) Date: Thu, 7 May 2026 18:22:28 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Andrew Morton , David Hildenbrand , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org Subject: [PATCH v5 01/28] mm: mempolicy: fix interleave index for unaligned VMA start Message-ID: <401fa82d946cd96ed200be5be4f911371e3f6f3c.1778192416.git.mst@redhat.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent The NUMA interleave index formula (addr - vm_start) >> shift gives wrong results when vm_start is not aligned to the folio size: the subtraction before the shift allows low bits to affect the result via borrows. Use (addr >> shift) - (vm_start >> shift) instead, which independently aligns both values before computing the difference. No functional change for current callers: the fix only affects NUMA interleave and weighted-interleave policies. The only current large-order caller is drm_pagemap which does not use NUMA interleave. All other callers use order 0 where the old and new formulas are equivalent. However subsequent patches in this series add large-order callers that pass unaligned fault addresses, making this fix necessary. Signed-off-by: Michael S. Tsirkin --- mm/mempolicy.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index f0f85c89da82..583b64f2b4d3 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2043,7 +2043,8 @@ struct mempolicy *get_vma_policy(struct vm_area_struct *vma, if (pol->mode == MPOL_INTERLEAVE || pol->mode == MPOL_WEIGHTED_INTERLEAVE) { *ilx += vma->vm_pgoff >> order; - *ilx += (addr - vma->vm_start) >> (PAGE_SHIFT + order); + *ilx += (addr >> (PAGE_SHIFT + order)) - + (vma->vm_start >> (PAGE_SHIFT + order)); } return pol; } -- MST