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Thu, 24 Sep 2026 08:57:05 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id cC7UE+HltGo7eQAAD6G6ig (envelope-from ); Thu, 24 Sep 2026 08:57:05 +0000 Date: Thu, 24 Sep 2026 09:57:03 +0100 From: Pedro Falcato To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/vma: predicate setting mmap_prepare VMA fields on new vma alloc Message-ID: References: <20260923-fix-mmap-prepare-overwrite-v1-1-3b3f1bfcdf5e@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923-fix-mmap-prepare-overwrite-v1-1-3b3f1bfcdf5e@kernel.org> X-Rspamd-Action: no action X-Stat-Signature: brs7ycgfdn1hprowmc876zx4nqxdte9t X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1771F80003 X-HE-Tag: 1790240235-364672 X-HE-Meta: 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 FRnIfNA9 61m9K9jif8fhPuQX2onoBy3iuS17Z2B5yKZyxFKMQKk5SVib1epPU/XuvwLkrw6/MwyIUeFrvV9oV9ZaQWA2sqjgMmW7UyZTb6Y0jxIJqaiVcPRRhNC/IvFWC/FCDFLNGImpgem2X01jbvfs8/CMOQ6MO3B4k+qy0ft3tXcNz1pWNHhkV8HTEz4c3hxR9WkkVTTjstTVrwWAuOGaZJ65scvdPS7+maagVS9wZydXztwvtb/vp7mEuHVBSlGDhK++gfuD7lIy+gDlykj2hksSJtHhFxbkcflr+WwfrV/gWHbC7MH/OmmOjkFZocw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 23, 2026 at 06:45:41PM +0100, Lorenzo Stoakes (ARM) wrote: > It only makes sense to manipulate VMA fields if a new VMA was allocated, > rather than merged. > > VMA merging does not compare vm_ops or vm_private_data, so a merged VMA > keeps its own, which is also what the legacy f_op->mmap path does since it > never touches an existing VMA. > > Currently, these fields will get overwritten by whatever state is > established in the mmap_prepare hook, and if the VMA was merged, > vm_ops->mapped will not have been called, so this could destructively clear > existing state without replacing it with anything valid. > > There is an implicit requirement that vm_private_data and vm_ops are > fungible across VMAs which means that losing the 'new' state is > fine. Hmm, can you explain how this is safe? I was wondering if _any_ kind of mismatch should be a WARN_ON (sounds like something odd is happening if they don't match). But if the new state is practically discardable, that doesn't make sense. -- Pedro