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[90.233.221.122]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-54ad64689eesm2075567e87.24.2025.03.27.06.05.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Mar 2025 06:05:51 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 27 Mar 2025 14:05:48 +0100 To: Ryan Roberts Cc: Catalin Marinas , Will Deacon , Pasha Tatashin , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , David Hildenbrand , "Matthew Wilcox (Oracle)" , Mark Rutland , Anshuman Khandual , Alexandre Ghiti , Kevin Brodsky , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 07/11] mm/vmalloc: Warn on improper use of vunmap_range() Message-ID: References: <20250304150444.3788920-1-ryan.roberts@arm.com> <20250304150444.3788920-8-ryan.roberts@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250304150444.3788920-8-ryan.roberts@arm.com> On Tue, Mar 04, 2025 at 03:04:37PM +0000, 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 subsequently call vunmap_range() on a > 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 just expected that callers will not do this. > > However, it would be useful to know if this happened in future; let's > add a warning to cover the eventuality. > > Reviewed-by: Anshuman Khandual > Reviewed-by: Catalin Marinas > 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); > -- > 2.43.0 > Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki