From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 26C8AC55ABA for ; Wed, 5 Aug 2026 11:33:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 326B06B0092; Wed, 5 Aug 2026 07:33:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2D0646B0093; Wed, 5 Aug 2026 07:33:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 172A16B0096; Wed, 5 Aug 2026 07:33:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id E40AD6B0092 for ; Wed, 5 Aug 2026 07:33:53 -0400 (EDT) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 7B2B8140465 for ; Wed, 5 Aug 2026 11:33:53 +0000 (UTC) X-FDA: 85067006346.11.F5E17B8 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.21]) by imf16.hostedemail.com (Postfix) with ESMTP id B4D24180009 for ; Wed, 5 Aug 2026 11:33:50 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=iY49MRD9; spf=pass (imf16.hostedemail.com: domain of matthew.brost@intel.com designates 198.175.65.21 as permitted sender) smtp.mailfrom=matthew.brost@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785929631; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=pkFLM2KZ6nsoGzQg5oepjsQvC9Ru7KiRDLQSg+5PJnk=; b=fao1xoOOb3jfq2fvnvnh3XOq6W7qOm+elmavTG/taXHrWYgQOcY2nrwwelzkT2AC0EkaCf IdERHsIW5Jd1a53/+vHB/yWwEtCqHGkrrnn0QdZWahrucd4ugg0iSbnINPUbMRF3ujls3Y C+tuo5ILQQ9BpWGWRuDq2GNiOQiHaFM= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785929631; b=etiEP6+c4UFNLcbFTk5v0/wuK+QS1Yuo6QRDQ362Mc/xM+yfFimDo+wRfuSghlCokLvcW4 +zvfMmGpL5wJ79Lcb1DKh6MFnrNACZJlTe+BmvvoxX5tC1UR6PsYaElu3jrsnXRjgtjInN ctZ020msS52WcH6R8a58U0GahzkCAPA= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=iY49MRD9; spf=pass (imf16.hostedemail.com: domain of matthew.brost@intel.com designates 198.175.65.21 as permitted sender) smtp.mailfrom=matthew.brost@intel.com; dmarc=pass (policy=none) header.from=intel.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1785929631; x=1817465631; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=ZxPU7quEySN5Hl4qRC5WeOO+MTXBZUcrGg6kx4/kNtY=; b=iY49MRD9UDgPHe0mDt6U1xFH9sxfnXCAL1C59qOpeahGvRHheOMBBtpz ffFLjmfuYObL48ECjsgRDsOh/X8KbPRoGQ7yXI7O7lh9g+cR0bP1qOTGP hqdeC28puFMgcP0waaGqNbgqOKnjS10VUNeXPIySrcgONXgVaeCHNLQTa HklWdE/1TtQbLZwgYW8dngd8bxIrj6HujXClQO2Ru2oRDBIzZZC/1lEb5 63vS7bIHyXjRQ46O7o6mX7cODB6dpIiKfG/4k2YP++GPQEHp8IKPCPEnQ jjpiDffjsf7vSGqWykfzme8PprPvFQdv00iVGzzgpjO6f1iK9wCD3CXcB A==; X-CSE-ConnectionGUID: H9iq8qsdRKCwb81A3/ca1g== X-CSE-MsgGUID: 9w1Ntr7WRoOFNpO5XqU5PQ== X-IronPort-AV: E=McAfee;i="6800,10657,11865"; a="86358181" X-IronPort-AV: E=Sophos;i="6.25,206,1779174000"; d="scan'208";a="86358181" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by orvoesa113.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2026 04:33:45 -0700 X-CSE-ConnectionGUID: TlTSTTbZQ92hntgr1WOfMQ== X-CSE-MsgGUID: X+D8wfZAS76OZrI13c7G0A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,206,1779174000"; d="scan'208";a="265289747" Received: from gsse-cloud1.jf.intel.com ([10.54.39.91]) by ORVIESA003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2026 04:33:45 -0700 From: Matthew Brost To: intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Balbir Singh , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= , Francois Dugast , stable@vger.kernel.org Subject: [PATCH 2/4] mm/migrate_device: Apply the fault reference to the correct folio Date: Wed, 5 Aug 2026 04:33:36 -0700 Message-Id: <20260805113338.3742178-3-matthew.brost@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260805113338.3742178-1-matthew.brost@intel.com> References: <20260805113338.3742178-1-matthew.brost@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B4D24180009 X-Stat-Signature: p9u6emz9eeq8eweph4ewt1799hyhghdm X-HE-Tag: 1785929630-385333 X-HE-Meta: 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 DV+Y3SQV 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: __migrate_device_pages() computed extra_cnt once, from the head page of the source folio, and then passed the same value to folio_migrate_mapping() for every one of the @nr sub-folios produced by migrate_vma_split_unmapped_folio(). The extra reference the CPU fault holds only exists on the single folio that ends up containing the fault page. Claiming it for all of them makes folio_migrate_mapping() expect one reference too many on every other sub-folio, so it returns -EAGAIN and MIGRATE_PFN_MIGRATE is cleared for them. Only the fault page would migrate; the remaining HPAGE_PMD_NR - 1 pages would be restored to device memory, and the faulting access would immediately fault again. Compute extra_cnt per sub-folio instead, comparing against the source page for that entry. While at it, use the sub-folio's own mapping rather than the mapping that was read from the pre-split folio. This has been latent so far because the split it depends on could never succeed while the fault reference was held. Fixes: 4265d67e405a ("mm/migrate_device: add THP splitting during migration") Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Balbir Singh Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: Thomas Hellström Cc: Francois Dugast Cc: dri-devel@lists.freedesktop.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Assisted-by: GitHub Copilot:claude-opus-5 Signed-off-by: Matthew Brost --- mm/migrate_device.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index d1d81bbbf795..65a6a15dba4d 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -1191,7 +1191,7 @@ static void __migrate_device_pages(unsigned long *src_pfns, struct page *page = migrate_pfn_to_page(src_pfns[i]); struct address_space *mapping; struct folio *newfolio, *folio; - int r, extra_cnt = 0; + int r; unsigned long nr = 1; if (!newpage) { @@ -1296,13 +1296,25 @@ static void __migrate_device_pages(unsigned long *src_pfns, BUG_ON(folio_test_writeback(folio)); - if (migrate && migrate->fault_page == page) - extra_cnt = 1; for (j = 0; j < nr && i + j < npages; j++) { - folio = page_folio(migrate_pfn_to_page(src_pfns[i+j])); + struct page *src_page = migrate_pfn_to_page(src_pfns[i+j]); + int extra_cnt = 0; + + folio = page_folio(src_page); newfolio = page_folio(migrate_pfn_to_page(dst_pfns[i+j])); - r = folio_migrate_mapping(mapping, newfolio, folio, extra_cnt); + /* + * The CPU fault holds an extra reference on the folio + * containing the fault page. @folio may have been + * split above, so the fault page only accounts for an + * extra reference on the folio it actually ended up + * in, not on every folio of the original THP. + */ + if (migrate && migrate->fault_page == src_page) + extra_cnt = 1; + + r = folio_migrate_mapping(folio_mapping(folio), newfolio, + folio, extra_cnt); if (r) src_pfns[i+j] &= ~MIGRATE_PFN_MIGRATE; else -- 2.34.1