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Wed, 28 Oct 2026 03:47:01 -0700 (PDT) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3ecd39a9sm28645811f8f.46.2026.10.28.03.47.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Oct 2026 03:47:00 -0700 (PDT) Message-ID: Date: Wed, 28 Oct 2026 11:46:59 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/vmalloc: drop VM_DMA_COHERENT from remap_vmalloc_range_partial To: Ye Liu , Andrew Morton , Uladzislau Rezki Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ye Liu References: <20261026-vmalloc_remap-v1-0-b7a907814e90@linux.dev> <20261026-vmalloc_remap-v1-1-b7a907814e90@linux.dev> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261026-vmalloc_remap-v1-1-b7a907814e90@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: bn3hziqfonjbd86wnqwdkdwd4okd3pyc X-Spam-Status: No, score=-14.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 6670340004 X-Rspam-User: X-HE-Tag: 1793184423-975276 X-HE-Meta: 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 Nl+XBsGt 0jT4m62mTuXpQhITQIM+vC7zMiAw67/9poZOV2sKV23+jlmTL/vbzOg3+Vht9nDYdDNCnLg5EASgZ9eoNvinebfay31/EX91AdbRq89Qx6sUObIq+mLBnCXyyOrgU8mSrMbk5oWLh103xp1Gv4AwHvTZ8HNTblsBkHZ/XeDVLmYTLEvYtcg+yGH2gYy6bkimglAMir1aXEJkDKvfFqy2ZDNZuB7zE35aAHkUY0Lbpv/bBuJ2xXr9kaQqy2aLbOSv2anbCiU1YjPtdagHTQ1Pw6OmG2DbvVwqGGmN8FRfRZzrEVxzrVlC5l813Br9PX2kzaSk8uPkVaiwDXeY4nfVa0vGr+Ao99j+ctHzS8D7/JnZJcT14A7oPll003aroeW5Vs3QCqDmcKu2Tu1kKobaKJwFW12q1PF2SKdNWnBKLylBP5X2XnnWNRUdH+mFJ4uCqgkQkFGJAmk7D/ji3NVkWCC+CKbkMVBh7xA/LMw2wySPndiY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/26/26 7:09 AM, Ye Liu wrote: > From: Ye Liu > > No caller maps a VM_DMA_COHERENT area through this path: such areas > come from dma_alloc_coherent() internals and are freed via vunmap(), > never through remap_vmalloc_range[_partial](); all 13 callers pass > vmalloc_user()/vmalloc()-backed addresses. > > The flag was added in commit fe9041c245196 ("vmalloc: lift the arm > flag for coherent mappings to common code") as a mechanical > translation of ARM's VM_ARM_DMA_CONSISTENT. It is also unsafe to keep > since commit 5ea8ec74c57c0 ("mm/vmalloc: free unused pages on > vrealloc() shrink"), which frees tail pages of non-VM_USERMAP areas > (VM_DMA_COHERENT is not in that skip-list): a shrunk-then-mapped area > would hit vmalloc_to_page()==NULL and vm_insert_page() would > dereference it unchecked. this isn't quite true, is it? the dma remap helpers vmap() without VM_MAP_PUT_PAGES, so nr_pages stays 0 and the shrink never frees anything there. > > Drop it so DMA-coherent areas can never enter the path. > > Signed-off-by: Ye Liu > --- > mm/vmalloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index db669103dc66..a888eca016a8 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -4894,7 +4894,7 @@ int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr, > if (!area) > return -EINVAL; > > - if (!(area->flags & (VM_USERMAP | VM_DMA_COHERENT))) > + if (!(area->flags & VM_USERMAP)) > return -EINVAL; > > if (check_add_overflow(size, off, &end_index) || > the change itself looks fine to me. -- cheers, jose a. p-a