From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 11B0227456 for ; Tue, 16 Jun 2026 09:15:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781601337; cv=none; b=ewqMfiLGhrngGjYKYs0cPzCOsrtlLd3rI7M+Ewhm1pVCVcBe/cdkfsdrXeovS8Tm4YFvqGEulLBVEZacsiHBX9w/bC36s4QI0ltCAZSonP/zoBYsc80mCNwgd1XVwm0C7xaM5OLnW99kbrI/2VMJip/NamNZQJLxWPBRMooUL0k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781601337; c=relaxed/simple; bh=9rOwkV9QgHXXFWQINk1wFiDvCLMF4fWHf7XAKv8LCdM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=fZ2je/orSbtPJLOYcmYOvjUXUZY4dcOwbg3wdpyMPjjW9exRD9WJ7n9n1M5zyqkOcV1j88BqFMB83kCIm7/8vaBXqJnJwMe4Z+miqgNYmtCnDXirSOjs1aGtD6aEqBheCk0HddAAR7kvvt9CgSxY9jN2MUJlvrgt1TAo1C/sLBA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=mbhUY4X0; arc=none smtp.client-ip=91.218.175.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="mbhUY4X0" 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=1781601333; 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=mWz7TCTy5BS+umTJteSAoLHr5Sx4WoMlxOW/yrqh7/E=; b=mbhUY4X0+dvUd/P+I4HklcbK2XloTs3O0XsQNEfyXzqirpxAIH5srCGFuZhwUm+urkYmJl SIt1RTZYCMnBaxCMx1kprVzNaP/bzSEEmxaPasE3XJ5BrAtF6ddxXz4sYrJginAwE8pQCM xTZ9nF+OlcX03ZQsB1lLpy59nVdgZDo= From: Lance Yang To: david@kernel.org, richard.weiyang@gmail.com Cc: balbirs@nvidia.com, akpm@linux-foundation.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, sj@kernel.org, ziy@nvidia.com, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, stable@vger.kernel.org, Lance Yang Subject: Re: [PATCH] mm/page_vma_mapped: revalidate and do proper check before return device-private pmd Date: Tue, 16 Jun 2026 17:15:22 +0800 Message-Id: <20260616091522.83765-1-lance.yang@linux.dev> In-Reply-To: <2d48ef0d-1110-4a9d-adcb-f701a1ce2cfa@kernel.org> References: <2d48ef0d-1110-4a9d-adcb-f701a1ce2cfa@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On Mon, Jun 15, 2026 at 01:58:15PM +0200, David Hildenbrand (Arm) wrote: >On 6/12/26 04:48, Wei Yang wrote: >> On Tue, May 12, 2026 at 08:55:47PM +0200, David Hildenbrand (Arm) wrote: >>> On 5/12/26 16:35, Wei Yang wrote: >>>> >>>> I tried to compress above logic like this, hope it could look cleaner. Emm ... spelling out the present/migration/device-private cases makes this easier to review, and avoids hiding future softleaf types behind pmd_is_valid_softleaf(), IMHO. So I'd prefer David's explicit version[1]. >>>> >>>> if (pmd_trans_huge(pmde) || pmd_is_valid_softleaf(pmde)) { >>>> unsigned long pfn; >>>> bool is_migration = pmd_is_migration_entry(pmde); >>>> bool for_migration = !!(pvmw->flags & PVMW_MIGRATION); >>>> >>>> if (is_migration != for_migration) >>>> return not_found(pvmw); >>>> >>>> if (pmd_trans_huge(pmde)) >>>> pfn = pmd_pfn(pmde); >>>> else >>>> pfn = softleaf_to_pfn(softleaf_from_pmd(pmde)); >>>> >>>> if (!check_pmd(pfn, pvmw)) >>>> return not_found(pvmw); >>>> } else if (!pmd_present(pmde)) { >>> >>> It's more compact, but not necessarily cleaner. In particular, I detest >>> pmd_trans_huge(), we should phase it out. >>> >>> if (pmd_present(pmde) && !pmd_leaf(pmde)) { >>> goto pte_table; >>> } else if (pmd_present(pmde) || pmd_is_valid_softleaf(pmde)) >>> >>> ... >>> >>> Might work as well. But once we add support for other softleaf types, we'll have >>> to touch it again. So I'd rather just list what we actually expect. >>> >> >> Hi, David > >Hi, > >> >> I may not follow you. Just want to confirm whether you prefer this goes as a >> fix first, or you prefer it goes as what you suggested here as a cleanup? > >I guess we should just do it properly when we're touching the code already. +1 to that ;) >Does that answer your question? Will you send a proper patch? Copied the diff from [1] below, with a couple of tiny nits inline. Feel free to grab any of this if it looks sane :) ---8<--- diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index a4d52fdb3056..de6a255cc847 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -242,40 +242,28 @@ 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); Could be const. + + if (!(pvmw->flags & PVMW_MIGRATION)) + return not_found(pvmw); + 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); Ditto. + 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) && @@ -285,6 +273,15 @@ 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))) Maybe worth a likely() here? The PMD normally shouldn't change under us. + return true; + spin_unlock(pvmw->ptl); + pvmw->ptl = NULL; + goto restart; +pte_table: if (!map_pte(pvmw, &pmde, &ptl)) { if (!pvmw->pte) --- [1] https://lore.kernel.org/linux-mm/0aab59b8-71c5-4059-8281-5dd876946528@kernel.org/ Cheers, Lance