From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75B623749F7; Fri, 2 Oct 2026 12:36:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790944572; cv=none; b=iAfKYjVrIywhOey1SluVdstiT0EifIDBP7/Fy30HPYzOrbxUp/dWq4+128/B7Of6C2qzM9rY8Wx0TqqLf9U0yCa+xvssMfV4bKdTUMtsPGVCrVVbPI1g4D1XqWz/bAqx0lG1QGat/E1Vu2sBiLIDB0PvGfFdX56nd2sTIrF8a50= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790944572; c=relaxed/simple; bh=zJdGvFnH9239op/29+uvDTEPTaYaAw90S9Cp4ykY2oc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PwojCdSfM2+t5YWTF3D61TJaZbgXcZj1oMeQwXyxfkTfXr2WVui1fWxY2dJJiKUHKkal5cxKVs8T/Yw4OKK+5UI/cLOogOpplqHiTazmbjMlOcNLQk90GH6G078ieuoY4FPx4Q7+Y/NaCBgCLpyg/4lU8USQsHqQNHgcE8/Y0Bs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Y04Ou6XX; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Y04Ou6XX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6D291F000FF; Fri, 2 Oct 2026 12:35:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790944571; bh=gHT1eHrCeRGheckcuVuH5tVn5htGR9KNUyLnh8eDOzU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Y04Ou6XX6SdMWUWTarLUhIsaN9w+3Pqeg8oUs/7OIb31JfWW0vUEVzkHQmEdDgjhX rMOXzqjsfTki350NeAiEQUKi4/Wmdue8la++1bjfwJl0sJt9qPFQ5jP+SuL7Z0VIrT fF/q64PoEK8zQ3Hm3rGDp9dID/9LqdMIt5ul42FGVvVWpLww9nxdUXfWoDIelUsaAq 8uHXbsWsAqgQEMs5R7FJEaINNCSu3zIGTrOrgwAyZ/QFIZy9pBQiDvOq7P6XMWUnTW K0nPXJCzRbOceqmLZfwrGmVvzEwYcn9zKQTP/XretUzMvEj70sWs0xCGSfo9UlqM4u t7IisLDZyS3qQ== Date: Fri, 2 Oct 2026 13:35:42 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Greg Kroah-Hartman , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Paul Moore , Stephen Smalley , Jaroslav Kysela , Takashi Iwai , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Doug Gilbert , "James E.J. Bottomley" , "Martin K. Petersen" , Jaya Kumar , Simona Vetter , Helge Deller , Sebastian Reichel , John Hubbard , Peter Xu , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Rik van Riel , Harry Yoo , Juri Lelli , Vincent Guittot , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Arnd Bergmann , Muchun Song , Oscar Salvador , "Matthew Wilcox (Oracle)" , Jan Kara , Marc Zyngier , Oliver Upton , Catalin Marinas , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , "David S. Miller" , Andreas Larsson , Alexander Viro , Christian Brauner , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Johannes Weiner , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chengming Zhou , Michal Hocko , Miklos Szeredi , Xu Xin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev Subject: Re: [PATCH v3 32/40] mm/uffd: use predicates for userfaultfd checks Message-ID: References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-32-4583d8a23bca@kernel.org> <72bbb616-e84e-4635-9d0a-336916db47e4@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <72bbb616-e84e-4635-9d0a-336916db47e4@kernel.org> On Fri, Oct 02, 2026 at 09:04:17AM +0200, David Hildenbrand (Arm) wrote: > On 9/17/26 18:22, Lorenzo Stoakes (ARM) wrote: > > Rather than directly checking VMA flags, use the newly introduced > > vma_is_kernel_owned() and vma_is_persistent() helpers in userfaultfd when > > assessing VMA suitability for userfaultfd and UFFDIO_MOVE. > > > > Update vma_move_compatible() so it's expressed in terms of VMA > > characteristics rather than arbitrary flags. > > > > Additionally, update the use of the deprecated VMA flag API when checking > > VMA_SHADOW_STACK_BIT. > > > > A VMA_IO_BIT check is no longer required but that is fine as a hard > > invariant has been established that only kernel-owned mappings may set > > VMA_IO_BIT so the check is now redundant. > > > > Signed-off-by: Lorenzo Stoakes (ARM) > > --- > > mm/userfaultfd.c | 21 +++++++++++++++------ > > 1 file changed, 15 insertions(+), 6 deletions(-) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 949017e60608..ddf0a4a3d399 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -1754,10 +1754,18 @@ static inline bool move_splits_huge_pmd(unsigned long dst_addr, > > } > > #endif > > > > -static inline bool vma_move_compatible(struct vm_area_struct *vma) > > +static inline bool vma_move_compatible(const struct vm_area_struct *vma) > > { > > - return !(vma->vm_flags & (VM_PFNMAP | VM_IO | VM_HUGETLB | > > - VM_MIXEDMAP | VM_SHADOW_STACK)); > > + /* uffd is generally incompatible with kernel-owned mappings. */ > > + if (vma_is_kernel_owned(vma)) > > + return false; > > + /* The shadow stack should not be written to by userspace. */ > > + if (vma_test_single_mask(vma, VMA_SHADOW_STACK)) > > + return false; > > + /* hugetlb mappings cannot be safely moved. */ > > + if (vma_is_hugetlb(vma)) > > + return false; > > + return true; > > return !vma_is_hugetlb(vma); Ack, done for v4. > > > } > > > > static int validate_move_areas(struct userfaultfd_ctx *ctx, > > @@ -2146,10 +2154,11 @@ static bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, > > { > > const struct vm_uffd_ops *ops = vma_uffd_ops(vma); > > > > - if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK)) > > + /* Non-persistent memory is inherently not controllable by userspace. */ > > + if (!vma_is_persistent(vma)) > > return false; > > Completely confusing. Just avoid the helper and open-code this here. See the other thread on this. I think with this as vma_is_volatile() this is a lot clearer. > > > - > > - if (!vma_is_hugetlb(vma) && (vma->vm_flags & VM_SPECIAL)) > > + /* The shadow stack should not be written to by userspace. */ > > + if (vma_test_single_mask(vma, VMA_SHADOW_STACK)) > > return false; > > > > vm_flags &= __VM_UFFD_FLAGS; > > > > Other stuff looks much better to me. Thanks! > > > -- > Cheers, > > David -- Cheers, Lorenzo