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 31392CD4F26 for ; Fri, 26 Jun 2026 11:32:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DD5A76B00B6; Fri, 26 Jun 2026 07:31:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D60B06B00BB; Fri, 26 Jun 2026 07:31:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C02296B00BF; Fri, 26 Jun 2026 07:31:58 -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 91C306B00B6 for ; Fri, 26 Jun 2026 07:31:58 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 08CCD8DC75 for ; Fri, 26 Jun 2026 11:31:58 +0000 (UTC) X-FDA: 84921849516.23.7694D57 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf14.hostedemail.com (Postfix) with ESMTP id 38A38100003 for ; Fri, 26 Jun 2026 11:31:56 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=DASHT9KJ; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782473516; b=U76v+iZ+tsZoJv0AQAj0Jtw1nyJKgBm9A5Uc8bYosT5XRbLkjmF14y72tiRp4V80CzbA3C 0il8Y6vNDcOQkf3k7is2KiSAq9bmZ7r6iiOUpGGTnRKnMqx3+zDZVMhBVR2iuX9HdcuBl3 Odi+DEUzQkD9T760Oac7duHa8sAQvkg= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782473516; 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=yXNMlFvQpQEhVOSE6W4KHuY5nfj10CNnD+tcN4AITD8=; b=CNf4LDSztAoqJD1tBgXMMW5KY1uW7iWvcuqbJ9xy5foq57JYyohHzNcLs8Hc39oC123dEK VKhX/wQcJ2rq86OewsiwWFYt4dluZG+FxttymWLiIxdeejXM8Y0HYPiH6NsNoQtTKukmTD PxRVOw2gQorSGezUHtPPyMtFtIvXMoM= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=DASHT9KJ; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 9A2D560098; Fri, 26 Jun 2026 11:31:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 18F3E1F000E9; Fri, 26 Jun 2026 11:31:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782473515; bh=yXNMlFvQpQEhVOSE6W4KHuY5nfj10CNnD+tcN4AITD8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=DASHT9KJdoV1oSrMo9dfIFwRJcr9M/y2wVWgR0pPxmHuHPaEV4U0YMehk9EzZXjZj ID5wUMJmxBxYC/f0YA4s0hTzql53FvCWOf5Z7K8DMb6mikXt7bEpHr2mn0ICKb7gQN zbsy+oAtwZd23G/IDzWxcBznyngSU2cx/Ff0Jw9m8BrNabEP6W57YoOV2ICKj5VZn0 JTQyE0Nuo5XGFJk/zDDA/99o5XfPoPm2cEcKgYm2xaz8i1BRZcYtTH6Ypepx5/OlJP F1bQCC6H+6DyvHXOcEQVW26rXuBOZzAMsd0i7QAMWo7JS/a2+bltrp68yQ9jCgbHSN I48MO+HIe9X+g== Message-ID: Date: Fri, 26 Jun 2026 13:31:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Patch mm-hotfixes v4] mm/page_vma_mapped: fix device-private PMD handling To: Lorenzo Stoakes Cc: Wei Yang , akpm@linux-foundation.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, ziy@nvidia.com, sj@kernel.org, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Lance Yang References: <20260624065353.1622-1-richard.weiyang@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 38A38100003 X-Stat-Signature: w8jst1omyz1ia484zy35zqifmuhfdfc8 X-HE-Tag: 1782473516-766590 X-HE-Meta: U2FsdGVkX18lt21KOiWsaCIfsvXl76upUSY1ekprReK3mAdiagaxFT1rBaIpOUlEdSUSjoljr/57PbM/rYIoKbajItCV3u6FPtptLKwHiHwXM0XnyWTPT6SUCju3oFfB27m7gTU7rJ2G/t5bjU+fIVk25GyB0ysglWnh2UKkEeOk8V2HFw5GB3xNl/eamtuuY+gHuFXjOHsJZWrcnkt2357VTk6Xvtv8BtCmYv3wHYPFQwANcYdSqbLQVfjxAZXEeEQDN4OzQj6hvwaOozArEPiWqyrH2uby64w1O+Ght+x00DXkkry6/X7/UcvtAAncs9yGVnRAiviS65WSTQ2ayst2nuMhKJGLQ2BjYXeNWqb/d/jEJhRY5YYMje1+RjFUyqMxJOK6Z3qLqCngSu+M/XyIaMRr0ZNY0haHrtDRk9KPdYCqayz0IaoO4YhPb7Gt0UkpWNAhGg1auMvPzXOM4k79F9gChMDaokhDHnu2wnvqwoAQ7fe0JAjOZnL/cJXfHc91Y0USrJjUsYwGhDuV0w6ylpF/xkktjz2RbfXJQrOWda0R26/Lc+swTo70WNFn2EGEIURnqGlUVaIl3gTW0U77PaQRSJ5V1YznVry+BvW1yE+bGmCa6wihD0cmrw4VHs1cYb8Qj0NvdhUTHGefMKbPJslAY+ZocQzVutUUJvZMHUByfecIfGAeaciG+1p2b1gA6uYFJkbuImJFSERD2FZdZkxUh2xSFxEU/Nlpwup4vmC8jTFckQ3/2iv3jJ24Kd5rJFM1fVfg+FZulaTkyjt/o8meba4hSG9l22gUWC3E4fB4gjpM4gxx4KGqlKhTTlZDTBY3GX4DzaU4nxT/HHCH32CJ5SQXaC6VxRWiHJ+blnOX2aDbFJvcIGIzTEAyI8H4ogpA1Orw8fZrjZ7cpZycPFWJiaaes+QA8OOJTiimh5YslzrTTpTNIz2hoFoL3ctDZVWo+OBwSzIXUZd heTwDbmm fo3br5gJWo/xEAu54wiTp7w6gJMROKXu0fOqNRLEkoR5USFAhPPGKDSHsyDarvIq3dvrnqWMDSwptKBLVpS+zjcUfKgE1R2duNjRfYPayT2Rv9ylCCHBVr1VbiSBE/Jv2MLRpocvkBUfDNNqqMGDgIRxhM0ZKOVXXCAd74C43cW9g3D2DmHpEwuLc2dxz9Z23T5Ip7/GvEL8AEa7m0TZITB2gIl809fO7NvkE7c9Ds0L/wNbjyzZOT+d/Yt3tuDpAkAU5WVjHvTBGGZlbQeTK8Galbsc1CKkRY4jXjqdEfEsfvnUcWggAlOu3ZiwaTRyN6bUNm7NoEhyLUR+nTGqr4NFHY5bAZfB97PlWM0aRpKS2HMM5zSP6S3YzBHUziyNdArvLcBiITEdfer4eMm8UBj5oDIFWvMoKjKIsD4wioDhehsEt8MWBzxI3FrN5JmI0UY9jnfX6LNz36K8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/26/26 12:42, Lorenzo Stoakes wrote: > On Fri, Jun 26, 2026 at 12:07:56PM +0200, David Hildenbrand (Arm) wrote: >> On 6/24/26 08:53, Wei Yang wrote: >>> Commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support >>> device-private entries") introduced the concept of device-private >>> PMD entries, but did not correctly update the rmap walk code to >>> account for them. >>> >>> As a result, when page_vma_mapped_walk() encounters device-private >>> PMD entries, it takes no action other than to acquire the PMD lock >>> and exit. >>> >>> However this is highly problematic for two reasons - firstly, >>> device private entries possess a PFN so check_pmd() needs to be >>> called to ensure an overlapping PFN range. >>> >>> Secondly, and more importantly, if PVMW_MIGRATION is set the >>> caller assumes the returned entry is a migration entry, resulting >>> in memory corruption when the caller tries to interpret the device >>> private entry as such. >>> >>> In addition, commit 146287290023 ("mm/huge_memory: implement >>> device-private THP splitting") allowed device private PMDs to be >>> split like THP mappings, but again did not update this code path. >>> >>> As a result, we might race a PMD split prior to acquiring the PMD >>> lock. >>> >>> This patch addresses all of these issues by invoking check_pmd(), >>> ensuring PMVW_MIGRATION is not set and checks whether a split raced >>> us we do for PMD THP and migration entries. >>> >>> Fixes: 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") >>> Cc: >>> Signed-off-by: Wei Yang >>> Suggested-by: David Hildenbrand >>> Cc: David Hildenbrand >>> Cc: Balbir Singh >>> Cc: SeongJae Park >>> Cc: Zi Yan >>> Cc: Lorenzo Stoakes >>> Cc: Lance Yang >>> >>> --- >>> v4: >>> * refine subject and commit log based on Lorenzo's suggestion >>> * put pmd device-private entry handling in its own if branch, >>> suggested by Lorenzo >>> >>> v3: >>> * remove cleanup part, only fix the issue for device-private entry >>> * refine user effect description based on Lorenzo's suggestion >>> >>> v2: https://lore.kernel.org/all/20260616063436.20455-1-richard.weiyang@gmail.com/T/#u >>> * specify the possible error case of current code and user visible effect >>> * besides fix, cleanup the pmd entry handling based on David's suggestion >>> >>> v1: https://lore.kernel.org/linux-mm/20260508013728.21285-1-richard.weiyang@gmail.com/ >>> --- >>> mm/page_vma_mapped.c | 20 +++++++++++++++----- >>> 1 file changed, 15 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >>> index 2ccbabfb2cc1..17dff8aab9f9 100644 >>> --- a/mm/page_vma_mapped.c >>> +++ b/mm/page_vma_mapped.c >>> @@ -269,14 +269,24 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >>> /* 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); >>> + } else if (pmd_is_device_private_entry(pmde)) { >>> + softleaf_t entry; >>> + >>> + pvmw->ptl = pmd_lock(mm, pvmw->pmd); >>> + pmde = *pvmw->pmd; >>> + entry = softleaf_from_pmd(pmde); >>> >>> - if (softleaf_is_device_private(entry)) { >>> - pvmw->ptl = pmd_lock(mm, pvmw->pmd); >>> + if (likely(softleaf_is_device_private(entry))) { >>> + if (pvmw->flags & PVMW_MIGRATION) >>> + return not_found(pvmw); >>> + if (!check_pmd(softleaf_to_pfn(entry), pvmw)) >>> + return not_found(pvmw); >>> return true; >>> } >>> - >>> + /* device-private pmd was split under us: handle on pte level */ >>> + spin_unlock(pvmw->ptl); >>> + pvmw->ptl = NULL; >>> + } else if (!pmd_present(pmde)) { >>> if ((pvmw->flags & PVMW_SYNC) && >>> thp_vma_suitable_order(vma, pvmw->address, >>> PMD_ORDER) && >> >> This is extremely hard to review given the existing crap handling here. I'm >> really sorry, but it makes my head hurt (I'm not kidding :) ). >> >> It's completely unclear why we only have to check for a subset of the cases >> after taking the lock. >> >> Could we simply extend the existing migration pmd handling and leave the >> !pmd_present() case for pmd_none()? >> >> That leaves no question to "which transitions are actually allowed", including >> "could we accidentally assume something is a page table when really it isn't". >> >> >> So what about something like the following? >> >> The "thp_migration_supported()" is not required when checking for >> pmd_is_migration_entry(), as that defaults to "false" when not compiled in. >> >> Untested: >> >> >> From 048ecd33673ec649e168fbbb97749a7c0e344fcd Mon Sep 17 00:00:00 2001 >> From: "David Hildenbrand (Arm)" >> Date: Fri, 26 Jun 2026 12:03:40 +0200 >> Subject: [PATCH] tmp >> >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/page_vma_mapped.c | 29 +++++++++++++++++------------ >> 1 file changed, 17 insertions(+), 12 deletions(-) >> >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >> index 2ccbabfb2cc17..ed2a23a90e8dd 100644 >> --- a/mm/page_vma_mapped.c >> +++ b/mm/page_vma_mapped.c >> @@ -243,21 +243,31 @@ 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)) { >> + if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || >> + pmd_is_device_private_entry(pmde)) { >> pvmw->ptl = pmd_lock(mm, pvmw->pmd); >> pmde = *pvmw->pmd; >> - if (!pmd_present(pmde)) { >> + if (pmd_is_migration_entry(pmde)) { >> softleaf_t entry; >> >> - if (!thp_migration_supported() || > > Do we care about this? Or is !tmp_migration_supported() -> implies you > wouldn't see a migration entry here anyway? Yeah, I noted above "The "thp_migration_supported()" is not required when checking for pmd_is_migration_entry(), as that defaults to "false" when not compiled in." Given that tmp_migration_supported() -> IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION);$ And pmd_is_migration_entry() -> softleaf_is_migration(softleaf_from_pmd(pmd)); whereby softleaf_from_pmd() only returns something non-none for CONFIG_ARCH_ENABLE_THP_MIGRATION. > > Maybe worth a VM_WARN_ON_ONCE()? I think it was primarily a a hack to slightly optimize code generated for !CONFIG_ARCH_ENABLE_THP_MIGRATION, not really something for correctness as it seems. So I think we can safely drop it. :) -- Cheers, David