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 B66C5487BE; Sun, 8 Feb 2026 09:54:58 +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=1770544498; cv=none; b=P2eDOs1Yha7LlVZXOkW4rOlwjcwLMgvEFEd4Jlk/OSz9TWZQE/HFDSyjjZxczx6UGKxSlDHEXekkAquP6k6/jNTHfVoBKUtptUvDP2pw3g8JagTGalYbfG5qvV8u7OwykdC7pKDij3LUcBSr0Ud29caQ06vyXZmMjb2nRsuFw1M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770544498; c=relaxed/simple; bh=VAJOqVbp2qDpQlX5+DAiOZoQgjFgIQczf/wGGbbFMDM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SdZYmLH58sM86WDJjVH1UkdWu1fR2h0odKI3LvtcDGlh3yvwfcylAEMfWKdv7QRNkkYe1LIheBH4AYNEktlKsl56yUBMQNt/QORokb7cxMcwz3GQZvk9Gdrlng0lkJb9XRCb0paTe+xfwAsFDvF6jNLFrbDTwDp/NF9WZ2dXLKQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CWSbWdyb; 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="CWSbWdyb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52B95C4CEF7; Sun, 8 Feb 2026 09:54:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770544498; bh=VAJOqVbp2qDpQlX5+DAiOZoQgjFgIQczf/wGGbbFMDM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CWSbWdybgY7UKB8egp0AumFhSehROCOkw9ZwBvyaB6Cr22MlGdRfkppkARTv7xewS CpHNebSqqlIlT+2SLxibHqkFfNvB/3ZZdew3XlQvCFNnuqqPmhBfuFp7R9CySFXrfm 298DS+S+pzIs5+sr4C9vPi49Cy65bixVDgtAu9fri2TmVXOjSpVLLVq0g1xGb3KAy/ cxKSP6KyriklgEyw6h2yYqJ1VyqiJTYr+y0Dlp7/qYd+3DvUc5p6FSoOtF1xV/oNnk p+S/n7dVe31j+VtH3WAvWIKC5ZWWfkwmqRMyDS3y1ZOJQLH2kXNHqk0KZGtvpD/W/h eGXZnCMt9eVXA== Date: Sun, 8 Feb 2026 11:54:47 +0200 From: Mike Rapoport To: Peter Xu Cc: linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC 04/17] userfaultfd: introduce mfill_get_vma() and mfill_put_vma() Message-ID: References: <20260127192936.1250096-1-rppt@kernel.org> <20260127192936.1250096-5-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=us-ascii Content-Disposition: inline In-Reply-To: Hi Peter, On Mon, Feb 02, 2026 at 04:49:09PM -0500, Peter Xu wrote: > Hi, Mike, > > On Tue, Jan 27, 2026 at 09:29:23PM +0200, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" > > > > Split the code that finds, locks and verifies VMA from mfill_atomic() > > into a helper function. > > > > This function will be used later during refactoring of > > mfill_atomic_pte_copy(). > > > > Add a counterpart mfill_put_vma() helper that unlocks the VMA and > > releases map_changing_lock. > > > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > mm/userfaultfd.c | 124 ++++++++++++++++++++++++++++------------------- > > 1 file changed, 73 insertions(+), 51 deletions(-) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 9dd285b13f3b..45d8f04aaf4f 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -157,6 +157,73 @@ static void uffd_mfill_unlock(struct vm_area_struct *vma) > > } > > #endif > > > > +static void mfill_put_vma(struct mfill_state *state) > > +{ > > + up_read(&state->ctx->map_changing_lock); > > + uffd_mfill_unlock(state->vma); > > + state->vma = NULL; > > +} > > + > > +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; > > + int err; > > + > > + /* > > + * Make sure the vma is not shared, that the dst range is > > + * both valid and fully within a single existing vma. > > + */ > > + dst_vma = uffd_mfill_lock(ctx->mm, state->dst_start, state->len); > > + if (IS_ERR(dst_vma)) > > + return PTR_ERR(dst_vma); > > + > > + /* > > + * If memory mappings are changing because of non-cooperative > > + * operation (e.g. mremap) running in parallel, bail out and > > + * request the user to retry later > > + */ > > + down_read(&ctx->map_changing_lock); > > + err = -EAGAIN; > > + if (atomic_read(&ctx->mmap_changing)) > > + goto out_unlock; > > + > > + err = -EINVAL; > > + > > + /* > > + * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but > > + * it will overwrite vm_ops, so vma_is_anonymous must return false. > > + */ > > + if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) && > > + dst_vma->vm_flags & VM_SHARED)) > > + goto out_unlock; > > + > > + /* > > + * validate 'mode' now that we know the dst_vma: don't allow > > + * a wrprotect copy if the userfaultfd didn't register as WP. > > + */ > > + if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) > > + goto out_unlock; > > + > > + if (is_vm_hugetlb_page(dst_vma)) > > + goto out; > > + > > + if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) > > + goto out_unlock; > > + if (!vma_is_shmem(dst_vma) && > > + uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) > > + goto out_unlock; > > IMHO it's a bit weird to check for vma permissions in a get_vma() function. > > Also, in the follow up patch it'll be also reused in > mfill_copy_folio_retry() which doesn't need to check vma permission. > > Maybe we can introduce mfill_vma_check() for these two checks? Then we can > also drop the slightly weird is_vm_hugetlb_page() check (and "out" label) > above. This version of get_vma() keeps the checks exactly as they were when we were retrying after dropping the lock and I prefer to have them this way to begin with. Later we can optimize this further after the dust settles after these changes. -- Sincerely yours, Mike.