From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 6F90018FDD5 for ; Fri, 7 Feb 2025 10:59:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738926001; cv=none; b=V2FOlAi6FmPnCplCVc0JL6AHE40IvvCHGY4o+SGLH5aKoiYCxuWk2AdL/FNuw2wJkXnPOje/3B24IbvyI3L/88rsu6LsMRaVHDGCY6ZuFaV1xY0t8ioO+1WvOJRpJpxhBCxo5fDyE+TxHX9WgRytdKJVecLujVGb7d6KlodUOVo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738926001; c=relaxed/simple; bh=//pQVvFwakmOqUSe9lGfJeVcFsPHvgzKBULKDjW+0hU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tm1yte2EnnQRJjCjbULeyN+s7HluSdqCUtq3Gz3KByetftZU+tl5EAjwImmGW8ZnUpjXBNoHxXn0NCbJHy3drTFR/oWzFMkSE8lB4BaAiGDNwenLpj4zyk6lPDiamCUQyCz2msmJWO4epVsL3Ab1kH/ICAAfE1vzHFtyAW4L4ms= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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