From nobody Mon Dec 1 22:36:21 2025 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 7EA76284883; Sun, 30 Nov 2025 11:18:44 +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=1764501524; cv=none; b=fkPNRrUMHwQ0c1JwjTeLTaELt44x8z+tDXozUOmg8A2m83awWVEPbCoJ4aPw2EfpcOmrn1Iwfm8bwrukudBloU7CqEdKF7n+rcXdMCQPCig/P8sp0ZQV9uEk67vVJ3lrQqewH6tAyPhXkA5NxMJmMr1scRkQUEjbUC2QCJeBMHM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764501524; c=relaxed/simple; bh=02TV+J21aRh8Y7GHD/quPCqz9iq/kEt5UBYeya9wXbk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JpwMmBfdoYLpIfkbjlpFF/sS8Up7fXVrveGXmyqGFVp/5x2raiY5/3swy88YUUypYpqntb3+jg13AJK+5CLHx2HDpF34/gun3CmBVPJtN17vf2f7vyeEUGqEJstX/Bpd7ASl6PmtdrKqCXz6KfFDjb1U1B+CJqToxBDXxsGcKRs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ha1VpMPt; 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="ha1VpMPt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE8BCC116B1; Sun, 30 Nov 2025 11:18:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764501523; bh=02TV+J21aRh8Y7GHD/quPCqz9iq/kEt5UBYeya9wXbk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ha1VpMPtHwMP3wcPEvYjsA/TXMScV1CPNuo/cC5Lu3DHFteFKJfHohkZUPQKy0KVH Jz15kY7NsoNnb2ifdGn0TVWvzfZyhLUyxG/9gwIiLivBDv2L+6NlrOm5HO7uAQ94VQ W43OZVat768mPtgYQldsGVGP+DmrQ8p0eWovjw7NXQrngRyeR+P0y9W6NokDg6dW8c WIecaNNGhqHcEWomX9JH4q2tcK5gXHSoUMT8n5MUCD6/p4ACgXX3jGubo4z7Y/nL96 nIZjMnQQSlLbYLMkRCy4SeLc/cuF1vSR8fRe2LRWKD8ko4jltWC0qCn1GUXPbYN46g CtYKcNVHiSLtg== 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 , Nikita Kalyazin , 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 v3 4/5] guest_memfd: add support for userfaultfd minor mode Date: Sun, 30 Nov 2025 13:18:11 +0200 Message-ID: <20251130111812.699259-5-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251130111812.699259-1-rppt@kernel.org> References: <20251130111812.699259-1-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: "Mike Rapoport (Microsoft)" userfaultfd notifications about minor page faults used for live migration and snapshotting of VMs with memory backed by shared hugetlbfs or tmpfs mappings as described in detail in commit 7677f7fd8be7 ("userfaultfd: add minor fault registration mode"). To use the same mechanism for VMs that use guest_memfd to map their memory, guest_memfd should support userfaultfd minor mode. Extend ->fault() method of guest_memfd with ability to notify core page fault handler that a page fault requires handle_userfault(VM_UFFD_MINOR) to complete and add implementation of ->get_folio_noalloc() to guest_memfd vm_ops. Reviewed-by: Liam R. Howlett Signed-off-by: Mike Rapoport (Microsoft) --- virt/kvm/guest_memfd.c | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index ffadc5ee8e04..dca6e373937b 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -4,6 +4,7 @@ #include #include #include +#include =20 #include "kvm_mm.h" =20 @@ -359,7 +360,15 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct v= m_fault *vmf) if (!((u64)inode->i_private & GUEST_MEMFD_FLAG_INIT_SHARED)) return VM_FAULT_SIGBUS; =20 - folio =3D kvm_gmem_get_folio(inode, vmf->pgoff); + folio =3D filemap_lock_folio(inode->i_mapping, vmf->pgoff); + if (!IS_ERR_OR_NULL(folio) && userfaultfd_minor(vmf->vma)) { + ret =3D VM_FAULT_UFFD_MINOR; + goto out_folio; + } + + if (PTR_ERR(folio) =3D=3D -ENOENT) + folio =3D kvm_gmem_get_folio(inode, vmf->pgoff); + if (IS_ERR(folio)) { int err =3D PTR_ERR(folio); =20 @@ -390,8 +399,30 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct v= m_fault *vmf) return ret; } =20 +#ifdef CONFIG_USERFAULTFD +static struct folio *kvm_gmem_get_folio_noalloc(struct inode *inode, + pgoff_t pgoff) +{ + struct folio *folio; + + folio =3D filemap_lock_folio(inode->i_mapping, pgoff); + if (IS_ERR_OR_NULL(folio)) + return folio; + + if (!folio_test_uptodate(folio)) { + clear_highpage(folio_page(folio, 0)); + kvm_gmem_mark_prepared(folio); + } + + return folio; +} +#endif + static const struct vm_operations_struct kvm_gmem_vm_ops =3D { .fault =3D kvm_gmem_fault_user_mapping, +#ifdef CONFIG_USERFAULTFD + .get_folio_noalloc =3D kvm_gmem_get_folio_noalloc, +#endif }; =20 static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) --=20 2.51.0