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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AB85FC55174 for ; Wed, 5 Aug 2026 19:35:49 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 78EC510EFC9; Wed, 5 Aug 2026 19:35:47 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="c4xhq9kk"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.9]) by gabe.freedesktop.org (Postfix) with ESMTPS id 453F210E0FB; Wed, 5 Aug 2026 19:35:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1785958544; x=1817494544; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=DwXjrp0YOMKqBIa0CyQY66LJvCKzj79JzvSlROjOOxA=; b=c4xhq9kkjFjzbnuCgiK9xudiX7k3PGRahsUiZeTYFoLxqVwOWQ7c7uSN 2cTkGMMRW23UYcT+wXe5u3Wa6W0sMsGCz5agbyfz59brvecH4NKA+beRA /mtNtn0eCbBWQeZzxB3UxywM4F7o0w0yStqvRJUikfboD7kc7ymbaTJAk +EKJm7QZsMY8nkuKImCckleaMZTYnkoX8cXDamCoYAOJXWnBI1A3qOmWC wYaoqMZDz5RwlLxzzsyw3OQ5HIXZzRXvrGhuK0IJrGoZmts5o2InslBeK CFIPGg7q/lI9t7ERT19m3RUgB+yVOzF/nDoITkbPEul4tsthYohodFTh2 Q==; X-CSE-ConnectionGUID: d6ro364NRLSuA7FccJzeOg== X-CSE-MsgGUID: fcKVpC24QYW5YDLR3rCrLg== X-IronPort-AV: E=McAfee;i="6800,10657,11866"; a="109332957" X-IronPort-AV: E=Sophos;i="6.25,207,1779174000"; d="scan'208";a="109332957" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by orvoesa101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2026 12:35:44 -0700 X-CSE-ConnectionGUID: CujDtT0BQmaBotcPTuJkwA== X-CSE-MsgGUID: sX6rfqqERo6FgsdinoenMQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,207,1779174000"; d="scan'208";a="285263527" Received: from gsse-cloud1.jf.intel.com ([10.54.39.91]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2026 12:35:43 -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 v2 3/5] mm/migrate_device: Apply the fault reference to the correct folio Date: Wed, 5 Aug 2026 12:35:34 -0700 Message-Id: <20260805193536.3756457-4-matthew.brost@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260805193536.3756457-1-matthew.brost@intel.com> References: <20260805193536.3756457-1-matthew.brost@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-xe-bounces@lists.freedesktop.org Sender: "Intel-xe" __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 142920a464d8..4ee09801efe6 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) { @@ -1301,13 +1301,25 @@ 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