From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 3D7DA3C8715; Fri, 27 Mar 2026 07:46:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774597588; cv=none; b=cFyHkjOdvT89rpWgBkIstSivVtxcsHtNo4Eqw+CYyRsBPvJIpupUyuBDcsxEi0ilAJsvCJ42WM02usiWVJkh3YKZ3HeX03w/zGCwCapDD5G5zZeNVKVWiWllLau0nvUUhLaVrB1Q0PJ/Vwx5hFXTFbSY2u7n6JMJlua8uN95S6I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774597588; c=relaxed/simple; bh=YpYLgI0jbsF+A0nzcAUua2nUX4/yXL66W0C5PJTgXrY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Nq/N6Hk/W5ipTmTN2rKtHSpzQUrnzY/sVq4SFk4UqLQQbDIegPjFQuM216G1g8KAf+YK++fiZLbbUbsNpqNJGYP5K+qcOSTwnsg+MPONoL6ERs8z3A6i0zONISXQm/MBS8as5FaaFu8SrXmvXlNhylzz4ZaqzxdgpIXseBDRQ/M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JAnfdjN+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JAnfdjN+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 39BD4C19423; Fri, 27 Mar 2026 07:46:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774597587; bh=YpYLgI0jbsF+A0nzcAUua2nUX4/yXL66W0C5PJTgXrY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JAnfdjN+EsvFi1j+dVGjzyHPyTGqTDMKTZrNVgQtgdS3xTJN/KeC6SXfA6DW6KjZ+ aXiEtUM3bJ0ki+Z9akOlTunEzzX5U9ssu8zkRelLpjeQHa/HwmIwwj6h10u5dOEg0M EKBK/9ZwAoABVZvbLpHEF0ii0f6vV3ud6iWKWuUuKizQooRHUkahfT6Z9o8xP7UzAv V7Ey/wrGk7siZDOJ5MJ/BLtJ5l6cix8sJsH1OOi+2j3uqZx/SfPbQJnE1wX5So5cdI qTCscyLEFql+4cw/7JjIAf1/JD2WybgTQS/Y93nhclmXbb4rNjhVp/Hxc+mgKRvhwF qjAqgYGSU/bnA== Date: Fri, 27 Mar 2026 10:46:15 +0300 From: Mike Rapoport To: James Houghton Cc: Andrew Morton , Andrea Arcangeli , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , "Liam R. Howlett" , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Michal Hocko , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 10/15] shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops Message-ID: References: <20260306171815.3160826-1-rppt@kernel.org> <20260306171815.3160826-11-rppt@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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Mar 26, 2026 at 06:13:37PM -0700, James Houghton wrote: > On Fri, Mar 6, 2026 at 9:19 AM Mike Rapoport wrote: > > > > From: "Mike Rapoport (Microsoft)" > > > > Add filemap_add() and filemap_remove() methods to vm_uffd_ops and use > > them in __mfill_atomic_pte() to add shmem folios to page cache and > > remove them in case of error. > > > > Implement these methods in shmem along with vm_uffd_ops->alloc_folio() > > and drop shmem_mfill_atomic_pte(). > > > > Since userfaultfd now does not reference any functions from shmem, drop > > include if linux/shmem_fs.h from mm/userfaultfd.c > > > > mfill_atomic_install_pte() is not used anywhere outside of > > mm/userfaultfd, make it static. > > > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > include/linux/shmem_fs.h | 14 ---- > > include/linux/userfaultfd_k.h | 21 +++-- > > mm/shmem.c | 148 ++++++++++++---------------------- > > mm/userfaultfd.c | 79 +++++++++--------- > > 4 files changed, 106 insertions(+), 156 deletions(-) > > > > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > > index a8273b32e041..1a345142af7d 100644 > > --- a/include/linux/shmem_fs.h > > +++ b/include/linux/shmem_fs.h > > @@ -221,20 +221,6 @@ static inline pgoff_t shmem_fallocend(struct inode *inode, pgoff_t eof) > > > > extern bool shmem_charge(struct inode *inode, long pages); > > > > -#ifdef CONFIG_USERFAULTFD > > -#ifdef CONFIG_SHMEM > > -extern int shmem_mfill_atomic_pte(pmd_t *dst_pmd, > > - struct vm_area_struct *dst_vma, > > - unsigned long dst_addr, > > - unsigned long src_addr, > > - uffd_flags_t flags, > > - struct folio **foliop); > > -#else /* !CONFIG_SHMEM */ > > -#define shmem_mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, \ > > - src_addr, flags, foliop) ({ BUG(); 0; }) > > -#endif /* CONFIG_SHMEM */ > > -#endif /* CONFIG_USERFAULTFD */ > > - > > /* > > * Used space is stored as unsigned 64-bit value in bytes but > > * quota core supports only signed 64-bit values so use that > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > > index 4d8b879eed91..bf4e595ac914 100644 > > --- a/include/linux/userfaultfd_k.h > > +++ b/include/linux/userfaultfd_k.h > > @@ -93,10 +93,24 @@ struct vm_uffd_ops { > > struct folio *(*get_folio_noalloc)(struct inode *inode, pgoff_t pgoff); > > /* > > * Called during resolution of UFFDIO_COPY request. > > - * Should return allocate a and return folio or NULL if allocation fails. > > + * Should allocate and return a folio or NULL if allocation > > + * fails. > > */ > > struct folio *(*alloc_folio)(struct vm_area_struct *vma, > > unsigned long addr); > > + /* > > + * Called during resolution of UFFDIO_COPY request. > > + * Should lock the folio and add it to VMA's page cache. > > I don't think "should lock the folio" is accurate. That sounds like > "it will call folio_lock()" but it actually calls > __folio_set_locked(). Maybe this is better: > > "Should only be called with a folio returned by alloc_folio() above. > The folio will set to locked." Yeah, sounds good. > > + * Returns 0 on success, error code on failure. > > + */ > > + int (*filemap_add)(struct folio *folio, struct vm_area_struct *vma, > > + unsigned long addr); > > @@ -404,6 +400,9 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, > > > > set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); > > > > + if (page_in_cache) > > + folio_unlock(folio); > > I don't really like doing the folio_unlock() *here*, I think it's > clearer if the callers (mfill_atomic_pte_continue() and > __mfill_atomic_pte()) unlocked the folio themselves. But that's just > my opinion. We already have page_in_cache here, so I'd prefer to keep a single folio_unlock() rather than add additional if (page_in_cache) in __mfill_atomic_pte(). > > + > > /* No need to invalidate - it was non-present before */ > > update_mmu_cache(dst_vma, dst_addr, dst_pte); > > ret = 0; > > @@ -836,41 +856,18 @@ extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx, > > > > static __always_inline ssize_t mfill_atomic_pte(struct mfill_state *state) > > { > > - struct vm_area_struct *dst_vma = state->vma; > > - unsigned long src_addr = state->src_addr; > > - unsigned long dst_addr = state->dst_addr; > > - struct folio **foliop = &state->folio; > > uffd_flags_t flags = state->flags; > > - pmd_t *dst_pmd = state->pmd; > > - ssize_t err; > > > > if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) > > return mfill_atomic_pte_continue(state); > > if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) > > return mfill_atomic_pte_poison(state); > > + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) > > + return mfill_atomic_pte_copy(state); > > + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) > > + return mfill_atomic_pte_zeropage(state); > > Thanks for this cleanup. :) > > > > > - /* > > - * The normal page fault path for a shmem will invoke the > > - * fault, fill the hole in the file and COW it right away. The > > - * result generates plain anonymous memory. So when we are > > - * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll > > - * generate anonymous memory directly without actually filling > > - * the hole. For the MAP_PRIVATE case the robustness check > > - * only happens in the pagetable (to verify it's still none) > > - * and not in the radix tree. > > - */ > > - if (!(dst_vma->vm_flags & VM_SHARED)) { > > - if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) > > - err = mfill_atomic_pte_copy(state); > > - else > > - err = mfill_atomic_pte_zeropage(state); > > - } else { > > - err = shmem_mfill_atomic_pte(dst_pmd, dst_vma, > > - dst_addr, src_addr, > > - flags, foliop); > > - } > > - > > - return err; > > + return -EOPNOTSUPP; > > WARN_ONCE() here I think. I'll add VM_WARN_ONCE() here. > Feel free to add: > > Reviewed-by: James Houghton Thanks! -- Sincerely yours, Mike.