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Mon, 26 Oct 2026 13:28:47 +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 KpbhAI9V32q2dgAAD6G6ig (envelope-from ); Mon, 26 Oct 2026 13:28:47 +0000 Date: Mon, 26 Oct 2026 13:28:45 +0000 From: Pedro Falcato To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Jakub =?utf-8?Q?Mat=C4=9Bna?= , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Luiz Capitulino , stable@vger.kernel.org Subject: Re: [PATCH] mm/vma: fix expansion of VMA_MIXEDMAP_BIT VMAs Message-ID: References: <20261023-vma-expansion-fix-v1-1-6142baf1f46b@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261023-vma-expansion-fix-v1-1-6142baf1f46b@kernel.org> X-Spamd-Result: default: False [-13.30 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[10]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[linux-foundation.org,infradead.org,kernel.org,google.com,gmail.com,kvack.org,vger.kernel.org,redhat.com]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -13.30 X-Spam-Level: X-Spam-Flag: NO On Fri, Oct 23, 2026 at 04:17:31PM +0100, Lorenzo Stoakes (ARM) wrote: > Commit ca3d76b0aa80 ("mm: add merging after mremap resize") combined > merging with expansion of mremap()'d VMAs, however it also unintentionally > disallowed the expansion of unmergeable VMAs. > > Previously it was possible to expand a mixed mapping which mremap() had > already ensured was a legal expansion. > > This is clearly seen in the mremap() logic, as it checks > vma_is_fixed_mapping() to determine legality of an expansion rather than > vma_can_merge(). > > Additionally, copy_vma() allows for a failed merge to result in a new VMA > being instantiated if MREMAP_MAYMOVE is specified. > > However, this is not attempted, as a failure in vma_merge_extend() is > assumed to be an -ENOMEM failure. > > Since vma_merge_extend() is used exclusively by mremap() to perform a merge > and/or expansion, resolve the issue by invoking vma_expand() for > unmergeable VMAs there. > > Explicitly assert that the VMA is both non-fixed and a mixed mapping. > This provides double insurance against broken changes in future. > > Note that khugepaged_enter_vma() (which vma_merge_new_range() runs) is > redundant in this case, as a mixed mapping is not subject to khugepaged. > > Also update the VMA userland tests to add a required predicate. > > Reported-by: Luiz Capitulino > Closes: https://lore.kernel.org/all/20261023023106.515365-1-luizcap@redhat.com/ > Fixes: ca3d76b0aa80 ("mm: add merging after mremap resize") > Cc: stable@vger.kernel.org > Signed-off-by: Lorenzo Stoakes (ARM) As much as I think this is smelly and filesystems really shouldn't be using MIXEDMAP: Reviewed-by: Pedro Falcato -- Pedro