From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4257CE95A8E for ; Mon, 9 Oct 2023 10:58:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346016AbjJIK62 (ORCPT ); Mon, 9 Oct 2023 06:58:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53838 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346133AbjJIK61 (ORCPT ); Mon, 9 Oct 2023 06:58:27 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BD4E49C; Mon, 9 Oct 2023 03:58:25 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15177C433C8; Mon, 9 Oct 2023 10:58:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1696849105; bh=pFDYRue/bKj9ILdCpjBIpmgz7Ku880Uz+C01332gWuE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DZye6kFSL5tEFdCjs6MTkk47EvSnsY2Nre6JIrO0oUkmZGhBkTxD4fw/6M2ik+6UH OBaW2AcdSVzxvRAfU1YsDqLBjItnHo70Xgcre3gbmhvUWUzhYCbuvppcC8n6ovUbbA d2gaYsklkkBN+k3GvWEybOTdQ5C1+tnV5e94K8VhIoaemsBCW2K8ZjCL2ZXvcf16s1 5SaqClDch5QdecmGk5sGuuGEFSyBsRwtoOfrh0YVFUehMqY0IeJyh+z38Y0DD48uJL 38td8l2QsNxmDuvBATmuYgSS5bspoLX52/Z+cHkY3hZwtfyLyK+leO2tkdvVDxhbvJ 4GwmYAnYaJZTw== Date: Mon, 9 Oct 2023 12:58:21 +0200 From: Alejandro Colomar To: Mike Rapoport Cc: Axel Rasmussen , Peter Xu , linux-man@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 05/10] ioctl_userfaultfd.2: describe two-step feature handshake Message-ID: References: <20230919190206.388896-1-axelrasmussen@google.com> <20230919190206.388896-6-axelrasmussen@google.com> <20231009084247.GI3303@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="W7HwIlpxFh93S0s/" Content-Disposition: inline In-Reply-To: <20231009084247.GI3303@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org --W7HwIlpxFh93S0s/ Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Date: Mon, 9 Oct 2023 12:58:21 +0200 From: Alejandro Colomar To: Mike Rapoport Cc: Axel Rasmussen , Peter Xu , linux-man@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 05/10] ioctl_userfaultfd.2: describe two-step feature handshake Hi Mike, On Mon, Oct 09, 2023 at 11:42:47AM +0300, Mike Rapoport wrote: > On Tue, Sep 19, 2023 at 12:02:01PM -0700, Axel Rasmussen wrote: > > Fully describe how UFFDIO_API can be used to perform a two-step feature > > handshake, and also note the case where this isn't necessary (programs > > which don't depend on any extra features). > >=20 > > This lets us clean up an old FIXME asking for this to be described. > >=20 > > Signed-off-by: Axel Rasmussen >=20 > Reviewed-by: Mike Rapoport (IBM) Since v2 is unchanged, I've added this tag. Thanks for the review! Cheers, Alex >=20 > > --- > > man2/ioctl_userfaultfd.2 | 37 +++++++++++++++++++++---------------- > > 1 file changed, 21 insertions(+), 16 deletions(-) > >=20 > > diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 > > index 339adf8fe..e91a1dfc8 100644 > > --- a/man2/ioctl_userfaultfd.2 > > +++ b/man2/ioctl_userfaultfd.2 > > @@ -83,7 +83,6 @@ struct uffdio_api { > > The > > .I api > > field denotes the API version requested by the application. > > -.PP > > The kernel verifies that it can support the requested API version, > > and sets the > > .I features > > @@ -93,6 +92,25 @@ fields to bit masks representing all the available f= eatures and the generic > > .BR ioctl (2) > > operations available. > > .PP > > +After Linux 4.11, > > +applications should use the > > +.I features > > +field to perform a two-step handshake. > > +First, > > +.BR UFFDIO_API > > +is called with the > > +.I features > > +field set to zero. > > +The kernel responsds by setting all supported feature bits. s/responsds/responds/ amended. > > +.PP > > +Applications which do not require any specific features > > +can begin using the userfaultfd immediately. > > +Applications which do need specific features > > +should call > > +.BR UFFDIO_API > > +again with a subset of the reported feature bits set > > +to enable those features. > > +.PP > > Before Linux 4.11, the > > .I features > > field must be initialized to zero before the call to > > @@ -102,24 +120,11 @@ and zero (i.e., no feature bits) is placed in the > > field by the kernel upon return from > > .BR ioctl (2). > > .PP > > -Starting from Linux 4.11, the > > -.I features > > -field can be used to ask whether particular features are supported > > -and explicitly enable userfaultfd features that are disabled by defaul= t. > > -The kernel always reports all the available features in the > > -.I features > > -field. > > -.PP > > -To enable userfaultfd features the application should set > > -a bit corresponding to each feature it wants to enable in the > > -.I features > > -field. > > -If the kernel supports all the requested features it will enable them. > > -Otherwise it will zero out the returned > > +If the application sets unsupported feature bits, > > +the kernel will zero out the returned > > .I uffdio_api > > structure and return > > .BR EINVAL . > > -.\" FIXME add more details about feature negotiation and enablement > > .PP > > The following feature bits may be set: > > .TP > > --=20 > > 2.42.0.459.ge4e396fd5e-goog > >=20 > >=20 >=20 > --=20 > Sincerely yours, > Mike. --=20 --W7HwIlpxFh93S0s/ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEE6jqH8KTroDDkXfJAnowa+77/2zIFAmUj3M0ACgkQnowa+77/ 2zIljg/+O+XKXPmc+OxbhyCJMh2jHqOEpdFbUq6rqZM6ZkTGGSD+G4lM4tN7QNvd 9UYN/jrxFq/Og4zpCYULSxSqYwgnKC25e3l2KNK0wT49D/T05vl/Fq2zQSD7lL2/ 303w2aAKijCdicWZumFytoUxAVybgHvsDGqgyq65w57muAWV+mSQjIQYnpXIvBKw uA1wncaMpXTU0CG7uehIGbudIRrc1FpmNp1yPjSMyCeN8LucS8xTOwDOaf1a1Q4L X4pgP/sr8t2uKC/1M9rnaA8GvhZp9vwxHBJxBvKyVhmkoiD8Fc15AtjI+OBKuo60 6Wh2jsrKQZsSeuYU/pITUO2XszbckymBatAIQkAbMPsQODthglIfb59GGCTxLoVU MJ88Pguc/WaSFz06T+AErgJaT94dnup4o2oDSloeQ+etRR0Ooqf5Dsm2cImRoIMt wKwYcJuYivqex+y85tBiD3UMIrKzpyyb3oTaYEfHMWpAzQnUYS7HJ0TAEW+pLF+f g8G8SohJkpxpkZ4SQKfs719tCB7qkUR0ToQhi18q2vGaQMjbFU48xZKidyV8bBju HwU2DpsYG6Iw0F7K1dcF3lACdvMhcdbOLygcM+tSDGD2asntQ6qEMn4EjgX18fCg kOLjOIYUJRaGMWxRBetts4DI41BN394UznxLu93XjJ+WVdSwV3k= =BdwT -----END PGP SIGNATURE----- --W7HwIlpxFh93S0s/--