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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=e0FGFPFZ; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B976A606A31A; Wed, 28 Oct 2026 08:43:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=e0FGFPFZ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 514F81F01825; Wed, 28 Oct 2026 08:43:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793177035; bh=LMwbpJ5FecMxJ5P7RbpHp11xGjgqCgb5rSN6ahzVqzY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=e0FGFPFZV0eKLLl32jk8I59lTEHQZEc8BJazgceNrvGoPpcwCu+4WvrvaSKgCd9WX IzOyxh5oVJv8Nwhf5GAZZMKstLdzYZ32czuXW9YbIlsF03Nm3316wrUZvZlxWKb6du 1PI+nawkxeyHD3BszZ03n5XTcheeQMbGpQFJ5Fs1Kcei/oeJBiMO3407pEVCoFxfRp w+UqDHQWXzrYlTaICvdhu1UyuH0FoWiPJyYnP7SA8hO6sA+LJGZky0dPGRW4/HJK6q FsTNGORi3mzq4nTdwM7L+t0toa2Kn+9DsarvP71ZTDicaw2OfwnPj1BKd7c89OkoOU Zl4DnismZRDgA== Message-ID: <829c448d-e6e2-4874-a166-7624e87489ef@kernel.org> Date: Wed, 28 Oct 2026 09:43:49 +0100 X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] RDMA/uverbs: Don't return the shared zero page from rdma_umap_fault() To: Zi Yan , Jason Gunthorpe , Leon Romanovsky Cc: linux-mm@kvack.org, Lorenzo Stoakes , Lance Yang , Kiryl Shutsemau , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261025-fix-rdma_umap_fault-zero-page-v1-1-186255624f1f@nvidia.com> <78802ed9-9cc6-41c4-b131-7c7d38f7ff39@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit >>> + /* >>> + * VMAs that cannot become writable map the page as a raw pfn, like >>> + * the device memory it replaces. The page lives as long as the file. >>> + */ >>> + if (!(vmf->vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) { >>> + ret = vmf_insert_pfn(vmf->vma, vmf->address, page_to_pfn(page)); >>> + goto out; >>> + } >>> + >>> + /* >>> + * This VMA is forced to always be shared so this doesn't have >>> + * to worry about COW. >>> + */ >>> + vmf->page = page; >>> + get_page(page); >> >> >> This split handling is pretty horrible TBH. >> >> In once case we take a reference in the other not? >> >> Why not perform a PFN mapping in any case? > > For writable path, a new vmf_insert_pfn_mkwrite() is needed, so it was > not fixed. I can fix that part as well. We should do that; returning kernel allocations from this function in ->fault is bad. How urgent is this fix here? (can it actually be triggered?Specific hardware?) > > The read-only zero page part might need more attention, since > we just prevented vmf_insert_pfn_prot() from using zero_page. Do we want > to add the support for rdma_umap_fault()? We just have to make sure that we cannot install it writable etc. But that's not a concern. Just have to be careful :) > >> >> (Does GUP have to work on these things?) > > These are VM_PFNMAP mappings, I guess not. But I am not a GUP expert. So we installed folios with ->fault in VM_PFNMAP!?!?!?! That doesn't sound right :) -- Cheers, David