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s=arc-20220608; d=hostedemail.com; t=1738917690; a=rsa-sha256; cv=none; b=AMQyua3orGAJSgJSEQDhivzFGGaj33/7ywEdlvWpRW5s4+b96M6Pd+lJ645ecQ+6miB3RJ W6E2FP+tA/SUoebAcPJ2XKwOFeBkbHT3qmzafnwirOLp3Lu7jYAnRtsUSSpXNFNXXz7Tq1 +bjyRjYEINtB12Ss7SlljKTyS4UYTp0= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf18.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@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 602831063; Fri, 7 Feb 2025 00:41:52 -0800 (PST) Received: from [10.162.16.89] (a077893.blr.arm.com [10.162.16.89]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 68CBC3F5A1; Fri, 7 Feb 2025 00:41:24 -0800 (PST) Message-ID: <3bbae070-1ae3-4f5d-86ab-b3221425a1cb@arm.com> Date: Fri, 7 Feb 2025 14:11:21 +0530 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> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20250205151003.88959-11-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 160D31C0009 X-Rspamd-Server: rspam07 X-Stat-Signature: 1sy7jc6g38opa4f7h53jzpn5976xbyxo X-HE-Tag: 1738917689-853246 X-HE-Meta: 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 jeuSNSe9 MeDfMeHtZUlc2/qDk83o2yk88OAW0T1zvAXwY2EWFmm+BkzgNYluGEhrZZJUd6tRrVHmEkp+B4UzzIp74FcyC+JZ+dP1ezDVoNRXdFauQ2lvnZUc1YgZM2U9gphx4bsP41VVsj4QRLnKXRT0dk3DiehqGvetB7s9V5KIc5UYfVDMzmUTxMjVD5Af/9Nk6AXARAwqxMCY/CGp74ZzoMG5eyu4A87SoJRnnXMtM8LlxRT3iX+WJJpjH+QjoeA== 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 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 ?