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 16E57CCD199 for ; Fri, 17 Oct 2025 15:04:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 71C048E0047; Fri, 17 Oct 2025 11:04:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6F3608E003B; Fri, 17 Oct 2025 11:04:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 630BA8E0047; Fri, 17 Oct 2025 11:04:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 514EE8E003B for ; Fri, 17 Oct 2025 11:04:53 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id CCCD4140232 for ; Fri, 17 Oct 2025 15:04:52 +0000 (UTC) X-FDA: 84007928424.23.E50E686 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) by imf15.hostedemail.com (Postfix) with ESMTP id D556DA0002 for ; Fri, 17 Oct 2025 15:04:50 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=HgsDgMKr; spf=pass (imf15.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.183 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1760713491; a=rsa-sha256; cv=none; b=XJYQ6CC8ysZphDXiSVaPR+V5aF3uFsG2MLbbUMcaGyC2zzSySob76UWlAty9cGcLx79mss SJfjHldJYEjee8FpDmxzItyz1FQzCKh1PxvG68zrXsAVriT/fyKYs101cqQ6VP2PALAZZ2 iJBfHaiPvNo+TbKu55rDap5rpFg7yXc= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=HgsDgMKr; spf=pass (imf15.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.183 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1760713491; 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=6ipsUjbeu91dDs7Ml8KfMCH/cB+JE6gc+gafMQFlHgY=; b=LnkmuOsNLGpMGAMecYC02/+ABMRFCm2WtkgwkbHf88+oVkZwpaUGqHOUuUXoUNT0Ic7fb+ KTlLEzLEytN3f+rNk9o2nhMRxG9n+S7/6lWKIkdFlz1XdSRsjY7D0vYrLM8Ee4ceiydJPY jZr861Op8TfL4J5/q3JMZRKmjRI/D+c= Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1760713488; 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=6ipsUjbeu91dDs7Ml8KfMCH/cB+JE6gc+gafMQFlHgY=; b=HgsDgMKryhNnwMN/ITSI0mJHUPe1aoHFEettJVOvu5MMft480FW6TcOIQaa72BlvM81e4i BRsSKwH5txiZWj5M8cFMRqLtB0rcB4PJCSbMT6s6xtEvdawatH5R4wtdnpJiZ+qC5IIDJI GqkU/Enizl55v/oaRojGF1O2kM4n6ps= Date: Fri, 17 Oct 2025 23:04:05 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-new v2 1/1] mm/khugepaged: guard is_zero_pfn() calls with pte_present() Content-Language: en-US To: David Hildenbrand , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Wei Yang References: <20251017093847.36436-1-lance.yang@linux.dev> <1937040d-5e70-4d9a-b77a-261bf0f4994e@redhat.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <1937040d-5e70-4d9a-b77a-261bf0f4994e@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: nkqm7geg54jdypaxyh15yjqc7sftf3ww X-Rspamd-Queue-Id: D556DA0002 X-Rspamd-Server: rspam09 X-HE-Tag: 1760713490-963060 X-HE-Meta: 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 qMPiJJB6 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/10/17 22:51, David Hildenbrand wrote: > On 17.10.25 11:38, Lance Yang wrote: >> From: Lance Yang >> >> A non-present entry, like a swap PTE, contains completely different data >> (swap type and offset). pte_pfn() doesn't know this, so if we feed it a >> non-present entry, it will spit out a junk PFN. >> >> What if that junk PFN happens to match the zeropage's PFN by sheer >> chance? While really unlikely, this would be really bad if it did. >> >> So, let's fix this potential bug by ensuring all calls to is_zero_pfn() >> in khugepaged.c are properly guarded by a pte_present() check. >> >> Suggested-by: Lorenzo Stoakes >> Reviewed-by: Dev Jain >> Reviewed-by: Baolin Wang >> Reviewed-by: Wei Yang >> Signed-off-by: Lance Yang >> --- >> Applies against commit 0f22abd9096e in mm-new. >> >> v1 -> v2: >>   - Collect Reviewed-by from Dev, Wei and Baolin - thanks! >>   - Reduce a level of indentation (per Dev) >>   - https://lore.kernel.org/linux-mm/20251016033643.10848-1- >> lance.yang@linux.dev/ >> >>   mm/khugepaged.c | 29 ++++++++++++++++------------- >>   1 file changed, 16 insertions(+), 13 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index d635d821f611..648d9335de00 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -516,7 +516,7 @@ static void release_pte_pages(pte_t *pte, pte_t >> *_pte, >>           pte_t pteval = ptep_get(_pte); >>           unsigned long pfn; >> -        if (pte_none(pteval)) >> +        if (!pte_present(pteval)) >>               continue; > > > Isn't it rather that if we would ever get a !pte_none() && ! > pte_present() here, something would be deeply flawed? > > I'd much rather spell that out and do here > > VM_WARN_ON_ONCE(!pte_present(pteval)); > > keeping the original check. Right, it's much better to be loud with a VM_WARN if we see a weird PTE, as Dev also suggested :) > > >>           pfn = pte_pfn(pteval); >>           if (is_zero_pfn(pfn)) >> @@ -690,17 +690,18 @@ static void >> __collapse_huge_page_copy_succeeded(pte_t *pte, >>            address += nr_ptes * PAGE_SIZE) { >>           nr_ptes = 1; >>           pteval = ptep_get(_pte); >> -        if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { >> +        if (pte_none(pteval) || >> +            (pte_present(pteval) && is_zero_pfn(pte_pfn(pteval)))) { > > This now seems to be a common pattern now :) > > > Should we have a simple helper > > static inline void pte_none_or_zero(pte_t pte) > { >     if (pte_none(pte)) >         return true; >     return pte_present(pte) && is_zero_pfn(pte_pfn(pte) > } > > initially maybe local to this file? And yeah, that logic is crying out for a new helper. Thanks!