From nobody Wed Feb 11 01:25:39 2026 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 204FD299922; Tue, 27 Jan 2026 19:31:21 +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=1769542282; cv=none; b=U0TGe2UXb+XkcVL3GB3wN0Fh+cGKfXcsGYsmUUxl65ksqVMR6zaxnXGcSwZ5fp+NXTCT4ZUtyQmD5FpRfSjNvklAWaPGoU3ctTjgVq8+f9w0DT1XvMFNhU2yuIGYno4rOLfUirPZg5ryZg9aPWDIpiYfopBVWF74W1Zlt3/pGxo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769542282; c=relaxed/simple; bh=96EEwJcWySxO2R/2KP/gCzA6SPsvcN9sMFGfwSmvv8I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BKjA+sougm+gJbsZCK6etP+iGD3Ngewf0FtwrVxw1r0anOrcjVuLi07GHZ7rSf+APNviGmtSb+jLa4H1DtQSroUexk/cX1xNAqcukuPc01rlVAHH0BxGhI3umD9VuwtQnlOINASiVh7jOXEgtYHhW8nyiAM2q7bhIS+XX5+MGH4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZW1wjmlE; 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="ZW1wjmlE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF23CC116C6; Tue, 27 Jan 2026 19:31:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769542281; bh=96EEwJcWySxO2R/2KP/gCzA6SPsvcN9sMFGfwSmvv8I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZW1wjmlEaWOSdy5FnqJJ6HOmgWV7pu0s4MRk84xlIeo88QjzOqjdIYlrG7ljWeU0v MeVT/1r5gvKQ8hwIT2RBtV0wKCMd8ov24qkrjcRy4Vfh/Y21OxTvvwPWedf28sTtpo suFN5ZKjXWM1NKIUy+6Dpr+0RTJ2rjrKbQS/lNK/SjFllGnjxzucAuckujiOyB+4U9 ccJBVk/3++oHxXEHSESsxUT5xJTAVOyEPse6JLGhtLLEhZZ/XVVi8U9wBHMb6IXpTH /5+0b26eHzpI8qMV5AnhQOxvJp1yjrHIWrURA/5Ndiprz3rlpr6hJnVNc2kD2LXCFh tOhezlpGaLTpQ== From: Mike Rapoport To: linux-mm@kvack.org Cc: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH RFC 15/17] KVM: guest_memfd: implement userfaultfd missing mode Date: Tue, 27 Jan 2026 21:29:34 +0200 Message-ID: <20260127192936.1250096-16-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260127192936.1250096-1-rppt@kernel.org> References: <20260127192936.1250096-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Nikita Kalyazin userfaultfd missing mode allows populating guest memory with the content supplied by userspace on demand. Extend guest_memfd implementation of vm_uffd_ops to support MISSING mode. Signed-off-by: Nikita Kalyazin Co-developed-by: Mike Rapoport (Microsoft) Signed-off-by: Mike Rapoport (Microsoft) --- virt/kvm/guest_memfd.c | 60 +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 59 insertions(+), 1 deletion(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 087e7632bf70..14cca057fc0e 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -431,6 +431,14 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct v= m_fault *vmf) ret =3D VM_FAULT_UFFD_MINOR; goto out_folio; } + + /* + * Check if userfaultfd is registered in missing mode. If so, + * check if a folio exists in the page cache. If not, return + * VM_FAULT_UFFD_MISSING to trigger the userfaultfd handler. + */ + if (userfaultfd_missing(vmf->vma) && IS_ERR_OR_NULL(folio)) + return VM_FAULT_UFFD_MISSING; } =20 /* folio not in the pagecache, try to allocate */ @@ -507,9 +515,59 @@ static bool kvm_gmem_can_userfault(struct vm_area_stru= ct *vma, vm_flags_t vm_fla return true; } =20 +static struct folio *kvm_gmem_folio_alloc(struct vm_area_struct *vma, + unsigned long addr) +{ + struct inode *inode =3D file_inode(vma->vm_file); + pgoff_t pgoff =3D linear_page_index(vma, addr); + struct mempolicy *mpol; + struct folio *folio; + gfp_t gfp; + + if (unlikely(pgoff >=3D (i_size_read(inode) >> PAGE_SHIFT))) + return NULL; + + gfp =3D mapping_gfp_mask(inode->i_mapping); + mpol =3D mpol_shared_policy_lookup(&GMEM_I(inode)->policy, pgoff); + mpol =3D mpol ?: get_task_policy(current); + folio =3D folio_alloc_mpol(gfp, 0, mpol, pgoff, numa_node_id()); + mpol_cond_put(mpol); + + return folio; +} + +static int kvm_gmem_filemap_add(struct folio *folio, + struct vm_area_struct *vma, + unsigned long addr) +{ + struct inode *inode =3D file_inode(vma->vm_file); + struct address_space *mapping =3D inode->i_mapping; + pgoff_t pgoff =3D linear_page_index(vma, addr); + int err; + + __folio_set_locked(folio); + err =3D filemap_add_folio(mapping, folio, pgoff, GFP_KERNEL); + if (err) { + folio_unlock(folio); + return err; + } + + return 0; +} + +static void kvm_gmem_filemap_remove(struct folio *folio, + struct vm_area_struct *vma) +{ + filemap_remove_folio(folio); + folio_unlock(folio); +} + static const struct vm_uffd_ops kvm_gmem_uffd_ops =3D { - .can_userfault =3D kvm_gmem_can_userfault, + .can_userfault =3D kvm_gmem_can_userfault, .get_folio_noalloc =3D kvm_gmem_get_folio_noalloc, + .alloc_folio =3D kvm_gmem_folio_alloc, + .filemap_add =3D kvm_gmem_filemap_add, + .filemap_remove =3D kvm_gmem_filemap_remove, }; #endif /* CONFIG_USERFAULTFD */ =20 --=20 2.51.0