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 83989369D57; Mon, 24 Aug 2026 15:11:00 +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=1787584261; cv=none; b=YQNH+cV+wLEiWj7MfVlyOuYpcPDIqwY2N7v+KVDpJz8yRtkTKU21lfkl92rY4x+/hkaMjHAm4cIzZGVJ5av6Yi5W+wtyIyvj3tctdv3xp/RbO66nrHnnfTNgGeOV1sTG6J6OzkHPHtxRByi83AxL0AqqanuBtpqkf5q3oyfXba0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787584261; c=relaxed/simple; bh=N5HeBxgaLz7/XZFrGAR2Ht9zy4LD5buaaVV/LUpd5fM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WI0Vt+Cy/x5bXIVi36OKpk8Fl8oOYFsip68nEIsu0VnQ2dDvXAQGcfpYxAHPdJXV5a0zBpw+PfNhh0bfR0Sky4moKhnJGsxle0mHpcFvGrAkX1gp5klwImNNQEb9NA8R9BIKd8mKV61uIduqjN4brWT5iFTSt8b6rRFaffpcnA8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aIeM4nw9; 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="aIeM4nw9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2423E1F000E9; Mon, 24 Aug 2026 15:10:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787584260; bh=Wx9f9XPX6UaTsyTsSp+lWebUiETju9PeSHKWEVZrKvQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=aIeM4nw9zSLp14C7Qg/aoWJ+Gibkr1HmmR0ckBQ4y26T1NYNtGBzmDSU3/xnRFaoV TuzTZNLgmDM9Q08D5Yzggqivp3V83HsLluIKSwBD+aVrE53Ku2YeWV1SMVRw1b+oVv WlqOq3JhDUknsD4U/dUlvXguIpg2M9YY9kuprCHgTPYml9GsRiKR1abr4/MGUglhw8 P0swNBzh5TBanefQbSD7CTT9M15MwtjMlbZh8xrpLK5szSEfkcbGMw9vqK000/4003 /mbEjamc8pSlzLFaYVI9BuaqwBPBc18xTuyi5oze1LI6PTCMFPD1qLTgli+1JpTkhb q10MUO6pdJrJQ== Date: Mon, 24 Aug 2026 16:10:51 +0100 From: "Lorenzo Stoakes (ARM)" To: "Mike Rapoport (Microsoft)" Cc: Andrew Morton , David Hildenbrand , Baolin Wang , Barry Song , Dev Jain , Hugh Dickins , Jann Horn , Jason Gunthorpe , John Hubbard , Jonathan Corbet , Lance Yang , "Liam R. Howlett" , Masami Hiramatsu , Mathieu Desnoyers , Michal Hocko , Muchun Song , Nico Pache , Oscar Salvador , Pedro Falcato , Peter Xu , Ryan Roberts , Shakeel Butt , Shuah Khan , Steven Rostedt , Suren Baghdasaryan , Usama Arif , Vlastimil Babka , Zi Yan , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH 3/6] userfaultfd: use userfaultfd_*() helpers instead of open coded flag tests Message-ID: References: <20260823-uffd-vm-flags-v1-v1-0-3086981b33cf@kernel.org> <20260823-uffd-vm-flags-v1-v1-3-3086981b33cf@kernel.org> Precedence: bulk X-Mailing-List: linux-trace-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: <20260823-uffd-vm-flags-v1-v1-3-3086981b33cf@kernel.org> On Sun, Aug 23, 2026 at 03:17:40PM +0300, Mike Rapoport (Microsoft) wrote: > Move userfaultfd_{missing,wp,minor,rwp}() and userfaultfd_protected() > ahead of uffd_disable_huge_pmd_share() and uffd_disable_fault_around() > and make the latter two use the helpers rather than open coded VMA flag > masks. > > Convert open coded VMA flag test in mfill_get_vma() to userfaultfd_wp() > as well. It'd be better to do the moves and the reworks separately. We don't have a limit on patch count :) > > With every user of the per-VMA uffd modes going through the helpers, > their underlying representation can be changed in the next step. > > No functional change. There is a functional change, or at least seems to be, see below. > > Assisted-by: copilot:claude-opus-5 > Signed-off-by: Mike Rapoport (Microsoft) > --- > include/linux/userfaultfd_k.h | 70 +++++++++++++++++++++---------------------- > mm/userfaultfd.c | 2 +- > 2 files changed, 35 insertions(+), 37 deletions(-) > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index 3396d270b159..d8262e3dc134 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -168,42 +168,6 @@ static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, > return vma->vm_userfaultfd_ctx.ctx == vm_ctx.ctx; > } > > -/* > - * Never enable huge pmd sharing on some uffd registered vmas: > - * > - * - VM_UFFD_WP and VM_UFFD_RWP VMAs, because the write protect / access > - * tracking information is per pgtable entry. > - * > - * - VM_UFFD_MINOR VMAs, because otherwise we would never get minor faults for > - * VMAs which share huge pmds. (If you have two mappings to the same > - * underlying pages, and fault in the non-UFFD-registered one with a write, > - * with huge pmd sharing this would *also* setup the second UFFD-registered > - * mapping, and we'd not get minor faults.) > - */ > -static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) > -{ > - return vma_test_any_mask(vma, > - mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP, > - VMA_UFFD_MINOR)); > -} > - > -/* > - * Don't do fault around for WP, RWP or MINOR registered uffd range. For > - * MINOR registered range, fault around will be a total disaster and ptes can > - * be installed without notifications; for WP it should mostly be fine as long > - * as the fault around checks for pte_none() before the installation, however > - * to be super safe we just forbid it; for RWP, pre-faulted neighbours would > - * be indistinguishable from accessed pages in PAGEMAP_SCAN (PAGE_IS_ACCESSED) > - * and pollute the tracked working set, so each page must be populated by its > - * own fault. > - */ > -static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) > -{ > - return vma_test_any_mask(vma, > - mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP, > - VMA_UFFD_MINOR)); > -} > - > static inline bool userfaultfd_missing(const struct vm_area_struct *vma) > { > return vma_test_any_mask(vma, VMA_UFFD_MISSING); > @@ -235,6 +199,40 @@ static inline bool userfaultfd_protected(const struct vm_area_struct *vma) > return userfaultfd_wp(vma) || userfaultfd_rwp(vma); > } > > +/* > + * Never enable huge pmd sharing on some uffd registered vmas: > + * > + * - uffd-WP and uffd-RWP VMAs, because the write protect / access tracking > + * information is per pgtable entry. > + * > + * - uffd-MINOR VMAs, because otherwise we would never get minor faults for > + * VMAs which share huge pmds. (If you have two mappings to the same > + * underlying pages, and fault in the non-UFFD-registered one with a write, > + * with huge pmd sharing this would *also* setup the second UFFD-registered > + * mapping, and we'd not get minor faults.) > + */ > +static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) > +{ > + return userfaultfd_minor(vma) || userfaultfd_wp(vma) || > + userfaultfd_rwp(vma); > +} > + > +/* > + * Don't do fault around for WP, RWP or MINOR registered uffd range. For > + * MINOR registered range, fault around will be a total disaster and ptes can > + * be installed without notifications; for WP it should mostly be fine as long > + * as the fault around checks for pte_none() before the installation, however > + * to be super safe we just forbid it; for RWP, pre-faulted neighbours would > + * be indistinguishable from accessed pages in PAGEMAP_SCAN (PAGE_IS_ACCESSED) > + * and pollute the tracked working set, so each page must be populated by its > + * own fault. > + */ > +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) > +{ > + return userfaultfd_minor(vma) || userfaultfd_wp(vma) || > + userfaultfd_rwp(vma); This is changing the logic. Before we were testing only the flags, now we have: static inline bool userfaultfd_rwp(const struct vm_area_struct *vma) { /* * Callers gate PAGE_NONE usage on this; PAGE_NONE is a BUILD_BUG() * without CONFIG_ARCH_HAS_PTE_PROTNONE, so fold to false. */ if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE)) return false; return vma_test_single_mask(vma, VMA_UFFD_RWP); } I.e. adding in a CONFIG_ARCH_HAS_PTE_PROTNONE check. BTW side-note these: static inline bool userfaultfd_missing(const struct vm_area_struct *vma) { return vma_test_any_mask(vma, VMA_UFFD_MISSING); } static inline bool userfaultfd_wp(const struct vm_area_struct *vma) { return vma_test_any_mask(vma, VMA_UFFD_WP); } static inline bool userfaultfd_minor(const struct vm_area_struct *vma) { return vma_test_any_mask(vma, VMA_UFFD_MINOR); } Should all use vma_test_single_mask() really :) > +} > + > static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma, > pte_t pte) > { > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 74f04c323c50..32003aa04943 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -261,7 +261,7 @@ static int mfill_get_vma(struct mfill_state *state) > * validate 'mode' now that we know the dst_vma: don't allow > * a wrprotect copy if the userfaultfd didn't register as WP. > */ > - if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) > + if ((flags & MFILL_ATOMIC_WP) && !userfaultfd_wp(dst_vma)) > goto out_unlock; > > if (is_vm_hugetlb_page(dst_vma)) > > -- > 2.53.0 > -- Cheers, Lorenzo