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 E9D73CD98D2 for ; Tue, 16 Jun 2026 20:46:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DD3506B00AD; Tue, 16 Jun 2026 16:45:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D5D086B00AE; Tue, 16 Jun 2026 16:45:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C4BF26B00AF; Tue, 16 Jun 2026 16:45:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 94FB66B00AD for ; Tue, 16 Jun 2026 16:45:57 -0400 (EDT) Received: from smtpin08.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 0CC00165723 for ; Tue, 16 Jun 2026 20:45:57 +0000 (UTC) X-FDA: 84886957554.08.0BC0377 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) by imf10.hostedemail.com (Postfix) with ESMTP id F338AC0007 for ; Tue, 16 Jun 2026 20:45:54 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=BDLtvHYb; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf10.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.178 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1781642755; 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=a7Yshx7diMX1O/OKyuwR/SBp/Kaw8zYRlyF2SsJvqRA=; b=iF5Pq9SycnA+Vhn0NTwqRAe8b0Tf0sHtKIRu4E2EcRL/9nwQ/7jZl/KVGBkxVBCPuzT72E ZGdHeq0bPRhLVJhVZWzjlZP4wB3fVOW2PCYgRZYrhuQrAg7O7EUa0mznNBJXocDflSAFXb FSJ+PQedj9W6c86YBRfiUsqrNmkpsx0= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=BDLtvHYb; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf10.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.178 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1781642755; b=2PEltjTe7Zmn0YFIvqQ2W8N8EXGYPv3dM12h1KyqSfZO7pdgmtUduVQ1cgkIoKg8+Bt8uI YUvpTUskNzTJLY75WlE0auN2dxoPdqpX071taNftGIHJWOyg5ulLchtt2aJGB9BqLnaCI9 EUemfPYNsIODtumD4Jcxp3AxZebgWl8= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781613032; h=from:from: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; bh=a7Yshx7diMX1O/OKyuwR/SBp/Kaw8zYRlyF2SsJvqRA=; b=BDLtvHYbtbBl6jCK8W2J5U0MaZ+1oaEDCCnJQ5XN2nOHOb6aWrop/Ja302qc7D7mNgSFTC JhIIPs9BWClMLzVyKktOsLn4D0CWfbprCz/ctP+BoNqWfwJ0yJmum4cSwIH2ADDPypw0OF nlVgsdz7pcnHRW7oy9djaeQRtFiomBg= From: Lance Yang To: richard.weiyang@gmail.com Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, balbirs@nvidia.com, ziy@nvidia.com, sj@kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, stable@vger.kernel.org, Lance Yang Subject: Re: [Patch v2] mm/page_vma_mapped: revalidate and do proper check before return device-private pmd Date: Tue, 16 Jun 2026 20:30:01 +0800 Message-Id: <20260616123001.6501-1-lance.yang@linux.dev> In-Reply-To: <20260616063436.20455-1-richard.weiyang@gmail.com> References: <20260616063436.20455-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: 5igqz8nj3shwgbp5e7mtcfzck9tp8syi X-Rspamd-Queue-Id: F338AC0007 X-HE-Tag: 1781642754-490833 X-HE-Meta: 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 KqCIQrvh HpOsdI5ozJBzjslRNM4rV0C3ws2Tvd1VKXyrESiJP1TjN6NyyScb0KCQ3wDIZoGFlnY1n3jj+OLFXMQgK5sAK/5pWmHtyRYa2+DrP72SLRpIiyCWePh0rNb3n7lXOnjG4B45SeVVrEqjN4tNFOtVoV7ReJh3yNwe+ocEaADA1RO+OXhPSVotf/dXILGy8KIJxHOXzbE2fR0Ptwkuve2Ns9vNU4MTHNZcy4K9nIZPQyuz229C7rGsbTMikq9+zPfCybI7RNOVykc7NxDqu4gIqcu4gzIfzfqiY8zVafAiLYOHnNa/4oYIiFkkorzaB1LLlZGkUVPBM3+gx/UI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 16, 2026 at 06:34:36AM +0000, Wei Yang wrote: [...] >diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >index 2ccbabfb2cc1..21635fab209c 100644 >--- a/mm/page_vma_mapped.c >+++ b/mm/page_vma_mapped.c >@@ -243,40 +243,28 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > */ > pmde = pmdp_get_lockless(pvmw->pmd); > >- if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) { >- pvmw->ptl = pmd_lock(mm, pvmw->pmd); >- pmde = *pvmw->pmd; >- if (!pmd_present(pmde)) { >- softleaf_t entry; >- >- if (!thp_migration_supported() || >- !(pvmw->flags & PVMW_MIGRATION)) >- return not_found(pvmw); >- entry = softleaf_from_pmd(pmde); >- >- if (!softleaf_is_migration(entry) || >- !check_pmd(softleaf_to_pfn(entry), pvmw)) >- return not_found(pvmw); >- return true; >- } >- if (likely(pmd_trans_huge(pmde))) { >- if (pvmw->flags & PVMW_MIGRATION) >- return not_found(pvmw); >- if (!check_pmd(pmd_pfn(pmde), pvmw)) >- return not_found(pvmw); >- return true; >- } >- /* THP pmd was split under us: handle on pte level */ >- spin_unlock(pvmw->ptl); >- pvmw->ptl = NULL; >- } else if (!pmd_present(pmde)) { >- const softleaf_t entry = softleaf_from_pmd(pmde); >- >- if (softleaf_is_device_private(entry)) { >- pvmw->ptl = pmd_lock(mm, pvmw->pmd); >- return true; >- } >+ if (pmd_present(pmde)) { >+ if (!pmd_leaf(pmde)) >+ goto pte_table; >+ if (pvmw->flags & PVMW_MIGRATION) >+ return not_found(pvmw); >+ if (!check_pmd(pmd_pfn(pmde), pvmw)) >+ return not_found(pvmw); >+ } else if (pmd_is_migration_entry(pmde)) { >+ softleaf_t entry = softleaf_from_pmd(pmde); >+ >+ if (!(pvmw->flags & PVMW_MIGRATION)) >+ return not_found(pvmw); Looked at history a bit, and I wonder if this changed something old here ... Since 616b8371539a ("mm: thp: enable thp migration in generic path"), PMD migration handling took PTL before doing PVMW_MIGRATION/PFN checks, including not_found() cases. So lockless PMD read was just a filter ... With this fix, true case gets final pmd_same() check, but this not_found() case happens before taking PTL. So a !PVMW_MIGRATION walker could race with someone, e.g. remove_migration_pmd(): we make the not_found() decision from old PMD value that still says "migration", while real *pvmw->pmd may already be present again. We return without ever taking PTL :) Not sure about practical fallout, but should these PMD-level not_found() cases also take PTL and restart if PMD changed? >+ if (!check_pmd(softleaf_to_pfn(entry), pvmw)) >+ return not_found(pvmw); >+ } else if (pmd_is_device_private_entry(pmde)) { >+ softleaf_t entry = softleaf_from_pmd(pmde); > >+ if (pvmw->flags & PVMW_MIGRATION) >+ return not_found(pvmw); >+ if (!check_pmd(softleaf_to_pfn(entry), pvmw)) >+ return not_found(pvmw); >+ } else { > if ((pvmw->flags & PVMW_SYNC) && > thp_vma_suitable_order(vma, pvmw->address, > PMD_ORDER) && >@@ -286,6 +274,15 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > step_forward(pvmw, PMD_SIZE); > continue; > } >+ >+ /* Double-check under PTL that the PMD didn't change. */ >+ pvmw->ptl = pmd_lock(mm, pvmw->pmd); >+ if (pmd_same(pmde, pmdp_get(pvmw->pmd))) >+ return true; >+ spin_unlock(pvmw->ptl); >+ pvmw->ptl = NULL; >+ goto restart; >+pte_table: > if (!map_pte(pvmw, &pmde, &ptl)) { > if (!pvmw->pte) > goto restart; >-- >2.34.1 > Cheers, Lance