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 1E9C93FFAB0; Fri, 6 Mar 2026 17:19:16 +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=1772817556; cv=none; b=CKQl5Fj87rbRl3H4BZJezVhcn5Ab0/7f6wJIGcNQ40ySfPNyF5Z54QTc3WPaONb1SUBbcWA8blpCajSmZSQhQzkPoG4fWnqnsH0+vWKUSIzv0sUGV9a9kWE4wZCfXi2aBYnDo+Wn+n4enIRnLgrWB0a0XSiw87O0rfoTzKLbzi8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772817556; c=relaxed/simple; bh=/0oNlg7fiYv022nxhnrVEoCU64mvQSwuS01zGUwLSsQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LxGfjO9xzgbFXBrFus4WMN8D8ztGQZOP/OJFBm96Jp8Uo+wZiLFZlNM9bFv3JKjXJDKDWgrCMo03BMOiWemIQTjxOhAsQvn4Bz3+B0SLNP0PtbzmY73kHamBvGUQOJhlP22DA0kKTMsyK+8RmJJ7FCywsmQ4oDbhrqmB/Nk+Vhk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=muO0cZ9r; 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="muO0cZ9r" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C953C19425; Fri, 6 Mar 2026 17:19:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772817556; bh=/0oNlg7fiYv022nxhnrVEoCU64mvQSwuS01zGUwLSsQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=muO0cZ9r+JBiL14XaQg5yw9LiQxGht59+apEgASJ2jR3LGxBAL2DsQtktz4uqSNqJ PkXHY04N+jL5v3G1MiqgSB6TbYGHqdBDSNAWY/aNjQxFtJSBEK0S22O0Y9wGNaJP17 In19HrRalevmDmNv5JBdAdSrm7ZCxnFnlXDD6srzq008AVs4fRuyfSBrSnPz+RHps5 1lQ+eH6EvtYxUo4N0NJqRwDFaYVUx8J7UuASQtNTGCIpna7WU5kGuspoZHDKNb5Pl7 dHZou2u+P4ijg57yiLXnqs07Bf41RlHmXBQ2PWIXWVKS2bD7DRkDLEXTYWCMpSCDpW ThUH3wtwpnBqA== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , 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: [PATCH v2 08/15] shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE Date: Fri, 6 Mar 2026 19:18:08 +0200 Message-ID: <20260306171815.3160826-9-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260306171815.3160826-1-rppt@kernel.org> References: <20260306171815.3160826-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Mike Rapoport (Microsoft)" When userspace resolves a page fault in a shmem VMA with UFFDIO_CONTINUE it needs to get a folio that already exists in the pagecache backing that VMA. Instead of using shmem_get_folio() for that, add a get_folio_noalloc() method to 'struct vm_uffd_ops' that will return a folio if it exists in the VMA's pagecache at given pgoff. Implement get_folio_noalloc() method for shmem and slightly refactor userfaultfd's mfill_get_vma() and mfill_atomic_pte_continue() to support this new API. Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/userfaultfd_k.h | 7 +++++++ mm/shmem.c | 15 ++++++++++++++- mm/userfaultfd.c | 32 ++++++++++++++++---------------- 3 files changed, 37 insertions(+), 17 deletions(-) diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 56e85ab166c7..66dfc3c164e6 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -84,6 +84,13 @@ extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason); struct vm_uffd_ops { /* Checks if a VMA can support userfaultfd */ bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags); + /* + * Called to resolve UFFDIO_CONTINUE request. + * Should return the folio found at pgoff in the VMA's pagecache if it + * exists or ERR_PTR otherwise. + * The returned folio is locked and with reference held. + */ + struct folio *(*get_folio_noalloc)(struct inode *inode, pgoff_t pgoff); }; /* A combined operation mode + behavior flags. */ diff --git a/mm/shmem.c b/mm/shmem.c index f2a25805b9bf..7bd887b64f62 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3295,13 +3295,26 @@ int shmem_mfill_atomic_pte(pmd_t *dst_pmd, return ret; } +static struct folio *shmem_get_folio_noalloc(struct inode *inode, pgoff_t pgoff) +{ + struct folio *folio; + int err; + + err = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + if (err) + return ERR_PTR(err); + + return folio; +} + static bool shmem_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags) { return true; } static const struct vm_uffd_ops shmem_uffd_ops = { - .can_userfault = shmem_can_userfault, + .can_userfault = shmem_can_userfault, + .get_folio_noalloc = shmem_get_folio_noalloc, }; #endif /* CONFIG_USERFAULTFD */ diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index b55d4a8d88cc..98ade14eaa5b 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -191,6 +191,7 @@ static int mfill_get_vma(struct mfill_state *state) struct userfaultfd_ctx *ctx = state->ctx; uffd_flags_t flags = state->flags; struct vm_area_struct *dst_vma; + const struct vm_uffd_ops *ops; int err; /* @@ -231,10 +232,12 @@ static int mfill_get_vma(struct mfill_state *state) if (is_vm_hugetlb_page(dst_vma)) goto out; - if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) + ops = vma_uffd_ops(dst_vma); + if (!ops) goto out_unlock; - if (!vma_is_shmem(dst_vma) && - uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) + + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) && + !ops->get_folio_noalloc) goto out_unlock; out: @@ -577,6 +580,7 @@ static int mfill_atomic_pte_zeropage(struct mfill_state *state) static int mfill_atomic_pte_continue(struct mfill_state *state) { struct vm_area_struct *dst_vma = state->vma; + const struct vm_uffd_ops *ops = vma_uffd_ops(dst_vma); unsigned long dst_addr = state->dst_addr; pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); struct inode *inode = file_inode(dst_vma->vm_file); @@ -586,16 +590,13 @@ static int mfill_atomic_pte_continue(struct mfill_state *state) struct page *page; int ret; - ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + if (!ops) + return -EOPNOTSUPP; + + folio = ops->get_folio_noalloc(inode, pgoff); /* Our caller expects us to return -EFAULT if we failed to find folio */ - if (ret == -ENOENT) - ret = -EFAULT; - if (ret) - goto out; - if (!folio) { - ret = -EFAULT; - goto out; - } + if (IS_ERR_OR_NULL(folio)) + return -EFAULT; page = folio_file_page(folio, pgoff); if (PageHWPoison(page)) { @@ -609,13 +610,12 @@ static int mfill_atomic_pte_continue(struct mfill_state *state) goto out_release; folio_unlock(folio); - ret = 0; -out: - return ret; + return 0; + out_release: folio_unlock(folio); folio_put(folio); - goto out; + return ret; } /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */ -- 2.51.0