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 9A23F13B29B for ; Thu, 13 Feb 2025 06:36:18 +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=1739428580; cv=none; b=YyGpyHA+IV++brZdt225lMCaK49WqfmRUkXWhRN8njLiY0T9xyXza0kJglGWWQxQN9mOUUqDlhtpOyCwIaPfsEhR9Pn/M7FzntNRr4tJ6cyhAPxASGrDPmxdJmsoxTGhLKGb2RDNLNmNaf09PeqxCPcRASaodACHRqCFOGOnoZU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739428580; c=relaxed/simple; bh=P+6n414RxyKfp4s5m1ZMMcWKMEscj1t0ZZK/rIeORQc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NnpeuU8T5E8f+qrq7jKYpHyF0inkTtHM7DMFdPmHHOpy66xJvalnaTbawBeZknH/X7qUUAau5JJdjpJUYSwXz7H36GMrf3RQX0EWeaJL4y6OBZNj3XH8kvQs2aotlAWHksB+pkzWRYcs+jkjZNJWyWQz/Fn8N8xgGEdbWwN1w5I= 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 5AD961756; Wed, 12 Feb 2025 22:36:38 -0800 (PST) Received: from [10.162.16.135] (a077893.blr.arm.com [10.162.16.135]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 502343F6A8; Wed, 12 Feb 2025 22:36:12 -0800 (PST) Message-ID: Date: Thu, 13 Feb 2025 12:06:09 +0530 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() To: Ryan Roberts , 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> Content-Language: en-US From: Anshuman Khandual In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/7/25 16:29, Ryan Roberts wrote: > 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. Understood, thanks !