From nobody Sat Apr 4 03:19:48 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 F0D1C35E92D; Thu, 2 Apr 2026 04:12:40 +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=1775103161; cv=none; b=gOFJjTZM87zMR0Jc6wD5L4C9QziwiT/Hkv5M6LXPtsvzD32c3Q3VcZM5EsyzSndmkbVPGv7PYH9VoOmq3ixS+pCr25qh1D+ZCUwj0Fx9iuXvSu37EBGfZz1ZkuKRu3MdfpjvGUJysOWxf/tACyUUlxdrGfHT5UIKyX22pLrOoyc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775103161; c=relaxed/simple; bh=5SzGyiFXZk7l7ucReQ40iRkaPGcy2CcX6r/21eMkk2I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Ju9ejd7nMf2gtQWF2iJWtmtou3wvxUMbR5LEiBpUf9dsFrq4PcgXjOIBLHJmLuz/aSXAtrtmOsqgY01WzV4MOMaqUA6UQMWuUX5SlXibnmAtf1DSX7ktBpF9fY8W65j2fHvE0fr20LgaI5dTsbkTc+ZCD1CC2Gb1fBM7nqRzyAk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nb8I1ZCl; 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="nb8I1ZCl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63406C19424; Thu, 2 Apr 2026 04:12:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775103160; bh=5SzGyiFXZk7l7ucReQ40iRkaPGcy2CcX6r/21eMkk2I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nb8I1ZClTDvPDGKxLBHAn3NCmEgGMU/AnhVCCtaCop4gpA26w+lGeVCMGevXI03Z7 ouBoPoNz1kFRSoUMyRWbj1Uwc6X15ppsOD1eoF7JwetBZZkgI1ZHeU62VnAhCzCpdV CgElsa9j93OX2uIsN8NVJVA1uAtcfmhXIYHd7hzfv5sMbFTLGYOor6KuIM1dcmms/p 2a0yzV0XuFg42PyKC66b+CK3kiM9NjbZh8qz+GI0RQX8A0MyIF++VDQ24nPRn6dKU8 da5kdRFrmmwwVlmhYmd9FFBvegTJuX2GBYV+d7U1E8pq8yGjXiCQIJ/Y82soByxhIj z1dktaok5sFiA== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Andrei Vagin , Axel Rasmussen , Baolin Wang , David Hildenbrand , Harry Yoo , Hugh Dickins , James Houghton , "Liam R. Howlett" , "Lorenzo Stoakes (Oracle)" , "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 v4 05/15] userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() Date: Thu, 2 Apr 2026 07:11:46 +0300 Message-ID: <20260402041156.1377214-6-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260402041156.1377214-1-rppt@kernel.org> References: <20260402041156.1377214-1-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)" Implementation of UFFDIO_COPY for anonymous memory might fail to copy data from userspace buffer when the destination VMA is locked (either with mm_lock or with per-VMA lock). In that case, mfill_atomic() releases the locks, retries copying the data with locks dropped and then re-locks the destination VMA and re-establishes PMD. Since this retry-reget dance is only relevant for UFFDIO_COPY and it never happens for other UFFDIO_ operations, make it a part of mfill_atomic_pte_copy() that actually implements UFFDIO_COPY for anonymous memory. As a temporal safety measure to avoid breaking biscection mfill_atomic_pte_copy() makes sure to never return -ENOENT so that the loop in mfill_atomic() won't retry copiyng outside of mmap_lock. This is removed later when shmem implementation will be updated later and the loop in mfill_atomic() will be adjusted. [akpm@linux-foundation.org: update mfill_copy_folio_retry()] Link: https://lkml.kernel.org/r/20260316173829.1126728-1-avagin@google.com Link: https://lkml.kernel.org/r/20260306171815.3160826-6-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) Signed-off-by: Andrew Morton --- mm/userfaultfd.c | 75 ++++++++++++++++++++++++++++++++---------------- 1 file changed, 51 insertions(+), 24 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index c6a38db45343..82e1a3255e1e 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -405,35 +405,63 @@ static int mfill_copy_folio_locked(struct folio *foli= o, unsigned long src_addr) return ret; } =20 +static int mfill_copy_folio_retry(struct mfill_state *state, struct folio = *folio) +{ + unsigned long src_addr =3D state->src_addr; + void *kaddr; + int err; + + /* retry copying with mm_lock dropped */ + mfill_put_vma(state); + + kaddr =3D kmap_local_folio(folio, 0); + err =3D copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); + kunmap_local(kaddr); + if (unlikely(err)) + return -EFAULT; + + flush_dcache_folio(folio); + + /* reget VMA and PMD, they could change underneath us */ + err =3D mfill_get_vma(state); + if (err) + return err; + + err =3D mfill_establish_pmd(state); + if (err) + return err; + + return 0; +} + static int mfill_atomic_pte_copy(struct mfill_state *state) { - struct vm_area_struct *dst_vma =3D state->vma; unsigned long dst_addr =3D state->dst_addr; unsigned long src_addr =3D state->src_addr; uffd_flags_t flags =3D state->flags; - pmd_t *dst_pmd =3D state->pmd; struct folio *folio; int ret; =20 - if (!state->folio) { - ret =3D -ENOMEM; - folio =3D vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma, - dst_addr); - if (!folio) - goto out; + folio =3D vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, state->vma, dst_addr); + if (!folio) + return -ENOMEM; =20 - ret =3D mfill_copy_folio_locked(folio, src_addr); + ret =3D -ENOMEM; + if (mem_cgroup_charge(folio, state->vma->vm_mm, GFP_KERNEL)) + goto out_release; =20 - /* fallback to copy_from_user outside mmap_lock */ - if (unlikely(ret)) { - ret =3D -ENOENT; - state->folio =3D folio; - /* don't free the page */ - goto out; - } - } else { - folio =3D state->folio; - state->folio =3D NULL; + ret =3D mfill_copy_folio_locked(folio, src_addr); + if (unlikely(ret)) { + /* + * Fallback to copy_from_user outside mmap_lock. + * If retry is successful, mfill_copy_folio_locked() returns + * with locks retaken by mfill_get_vma(). + * If there was an error, we must mfill_put_vma() anyway and it + * will take care of unlocking if needed. + */ + ret =3D mfill_copy_folio_retry(state, folio); + if (ret) + goto out_release; } =20 /* @@ -443,17 +471,16 @@ static int mfill_atomic_pte_copy(struct mfill_state *= state) */ __folio_mark_uptodate(folio); =20 - ret =3D -ENOMEM; - if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) - goto out_release; - - ret =3D mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, + ret =3D mfill_atomic_install_pte(state->pmd, state->vma, dst_addr, &folio->page, true, flags); if (ret) goto out_release; out: return ret; out_release: + /* Don't return -ENOENT so that our caller won't retry */ + if (ret =3D=3D -ENOENT) + ret =3D -EFAULT; folio_put(folio); goto out; } --=20 2.53.0