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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 1F3F8C02194 for ; Fri, 7 Feb 2025 11:01:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=bEyqjleM/WRbKW1ebONSnQcH9I0/t61hK4xp+wMk12w=; b=1lh1wgh8OVoJWcVFKZ0C8ZIORS 0la6sY+/ezgrDNw6gt2cregbtC9IfIEXfupbQsb50/13J8FU8/AgxOiVFgcB6K+cij9L+DTVrvymG lFALKmWI3cRON9RIhd9cLkmTgQTcVhehmUIW/wsw1YQWD/lOHAoZx2SBKaEaPQDRfdtoq1hYPadFV 9iBtR9aFqSoOGpjxt/j7itbV4I8N5aTCJAwDQzrvqQdziAeEx4P0e9ePgrU6RK0zIsUEAWUeg8zt+ ZEiRTzIZwVpMfvDU1PgclfO0jx0HUvaOG4o3dA7GznKAW4p5PE38Q6rra6Yu6LOmETxIYmnptVFv2 uIfnQn0Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tgM6w-00000009I2J-3DpQ; Fri, 07 Feb 2025 11:01:26 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tgM5X-00000009Hmy-1Jpj for linux-arm-kernel@lists.infradead.org; Fri, 07 Feb 2025 11:00:00 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9E81B113E; Fri, 7 Feb 2025 03:00:21 -0800 (PST) Received: from [10.57.81.111] (unknown [10.57.81.111]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AED2C3F63F; Fri, 7 Feb 2025 02:59:55 -0800 (PST) Message-ID: Date: Fri, 7 Feb 2025 10:59:53 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 10/16] mm/vmalloc: Warn on improper use of vunmap_range() Content-Language: en-GB To: Anshuman Khandual , Catalin Marinas , Will Deacon , Muchun Song , Pasha Tatashin , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Mark Rutland , Ard Biesheuvel , Dev Jain , Alexandre Ghiti , Steve Capper , Kevin Brodsky Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250205151003.88959-1-ryan.roberts@arm.com> <20250205151003.88959-11-ryan.roberts@arm.com> <3bbae070-1ae3-4f5d-86ab-b3221425a1cb@arm.com> From: Ryan Roberts In-Reply-To: <3bbae070-1ae3-4f5d-86ab-b3221425a1cb@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250207_025959_445209_DD16CDA3 X-CRM114-Status: GOOD ( 21.06 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 07/02/2025 08:41, Anshuman Khandual wrote: > On 2/5/25 20:39, Ryan Roberts wrote: >> A call to vmalloc_huge() may cause memory blocks to be mapped at pmd or >> pud level. But it is possible to subsquently call vunmap_range() on a > > s/subsquently/subsequently > >> sub-range of the mapped memory, which partially overlaps a pmd or pud. >> In this case, vmalloc unmaps the entire pmd or pud so that the >> no-overlapping portion is also unmapped. Clearly that would have a bad >> outcome, but it's not something that any callers do today as far as I >> can tell. So I guess it's jsut expected that callers will not do this. > > s/jsut/just > >> >> However, it would be useful to know if this happened in future; let's >> add a warning to cover the eventuality. > > This is a reasonable check to prevent bad outcomes later. > >> >> Signed-off-by: Ryan Roberts >> --- >> mm/vmalloc.c | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >> index a6e7acebe9ad..fcdf67d5177a 100644 >> --- a/mm/vmalloc.c >> +++ b/mm/vmalloc.c >> @@ -374,8 +374,10 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, >> if (cleared || pmd_bad(*pmd)) >> *mask |= PGTBL_PMD_MODIFIED; >> >> - if (cleared) >> + if (cleared) { >> + WARN_ON(next - addr < PMD_SIZE); >> continue; >> + } >> if (pmd_none_or_clear_bad(pmd)) >> continue; >> vunmap_pte_range(pmd, addr, next, mask); >> @@ -399,8 +401,10 @@ static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, >> if (cleared || pud_bad(*pud)) >> *mask |= PGTBL_PUD_MODIFIED; >> >> - if (cleared) >> + if (cleared) { >> + WARN_ON(next - addr < PUD_SIZE); >> continue; >> + } >> if (pud_none_or_clear_bad(pud)) >> continue; >> vunmap_pmd_range(pud, addr, next, mask); > Why not also include such checks in vunmap_p4d_range() and __vunmap_range_noflush() > for corresponding P4D and PGD levels as well ? The kernel does not support p4d or pgd leaf entries so there is nothing to check. Although vunmap_p4d_range() does call p4d_clear_huge(). The function is a stub and returns void (unlike p[mu]d_clear_huge()). I suspect we could just remove p4d_clear_huge() entirely. But that would be a separate patch to mm tree I think. For pgd, there isn't even an equivalent looking function. Basically at those 2 levels, it's always a table. Thanks, Ryan