linux-kernel - Re: [PATCH v2 08/14] mm/vmalloc: Warn on improper use of vunmap

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Message-ID: <Z7xgQr7_xivV849V@arm.com>
Date: Mon, 24 Feb 2025 12:04:18 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Will Deacon <will@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Kevin Brodsky <kevin.brodsky@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/14] mm/vmalloc: Warn on improper use of
 vunmap_range()

On Mon, Feb 17, 2025 at 02:08:00PM +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.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>