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 X-Spam-Level: X-Spam-Status: No, score=-5.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,URIBL_DBL_ABUSE_MALW,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE999C35240 for ; Fri, 31 Jan 2020 12:57:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE7EE20705 for ; Fri, 31 Jan 2020 12:57:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728634AbgAaM5s (ORCPT ); Fri, 31 Jan 2020 07:57:48 -0500 Received: from jabberwock.ucw.cz ([46.255.230.98]:48040 "EHLO jabberwock.ucw.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728514AbgAaM5r (ORCPT ); Fri, 31 Jan 2020 07:57:47 -0500 Received: by jabberwock.ucw.cz (Postfix, from userid 1017) id 930C61C228F; Fri, 31 Jan 2020 13:57:46 +0100 (CET) Date: Fri, 31 Jan 2020 13:57:31 +0100 From: Pavel Machek To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Peter Zijlstra , Fenghua Yu , Tony Luck , "David S. Miller" , Sasha Levin Subject: Re: [PATCH 4.19 36/55] drivers/net/b44: Change to non-atomic bit operations on pwol_mask Message-ID: <20200131125730.GA20888@duo.ucw.cz> References: <20200130183608.563083888@linuxfoundation.org> <20200130183615.120752961@linuxfoundation.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="9amGYk9869ThD9tj" Content-Disposition: inline In-Reply-To: <20200130183615.120752961@linuxfoundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --9amGYk9869ThD9tj Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu 2020-01-30 19:39:17, Greg Kroah-Hartman wrote: > From: Fenghua Yu >=20 > [ Upstream commit f11421ba4af706cb4f5703de34fa77fba8472776 ] This is not suitable for stable. It does not fix anything. It prepares for theoretical bug that author claims might be introduced to BIOS in future... I doubt it, even BIOS authors boot their machines from time to time. > Atomic operations that span cache lines are super-expensive on x86 > (not just to the current processor, but also to other processes as all > memory operations are blocked until the operation completes). Upcoming > x86 processors have a switch to cause such operations to generate a #AC > trap. It is expected that some real time systems will enable this mode > in BIOS. And I wonder if this is even good idea for mainline. x86 architecture is here for long time, and I doubt Intel is going to break it like this. Do you have documentation pointer?=20 > In preparation for this, it is necessary to fix code that may execute > atomic instructions with operands that cross cachelines because the #AC > trap will crash the kernel. How does single bit operation "cross cacheline"? How is this going to impact non-x86 architectures? > Since "pwol_mask" is local and never exposed to concurrency, there is > no need to set bits in pwol_mask using atomic operations. >=20 > Directly operate on the byte which contains the bit instead of using > __set_bit() to avoid any big endian concern due to type cast to > unsigned long in __set_bit(). What concerns? Is __set_bit() now useless and are we going to open-code it everywhere? Is set_bit() now unusable on x86? =09 Pavel =09 > Suggested-by: Peter Zijlstra > Signed-off-by: Fenghua Yu > Signed-off-by: Tony Luck > Signed-off-by: David S. Miller > Signed-off-by: Sasha Levin > --- > drivers/net/ethernet/broadcom/b44.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) >=20 > diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/b= roadcom/b44.c > index e445ab724827f..88f8d31e4c833 100644 > --- a/drivers/net/ethernet/broadcom/b44.c > +++ b/drivers/net/ethernet/broadcom/b44.c > @@ -1519,8 +1519,10 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppat= tern, u8 *pmask, int offset) > int ethaddr_bytes =3D ETH_ALEN; > =20 > memset(ppattern + offset, 0xff, magicsync); > - for (j =3D 0; j < magicsync; j++) > - set_bit(len++, (unsigned long *) pmask); > + for (j =3D 0; j < magicsync; j++) { > + pmask[len >> 3] |=3D BIT(len & 7); > + len++; > + } > =20 > for (j =3D 0; j < B44_MAX_PATTERNS; j++) { > if ((B44_PATTERN_SIZE - len) >=3D ETH_ALEN) > @@ -1532,7 +1534,8 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppatt= ern, u8 *pmask, int offset) > for (k =3D 0; k< ethaddr_bytes; k++) { > ppattern[offset + magicsync + > (j * ETH_ALEN) + k] =3D macaddr[k]; > - set_bit(len++, (unsigned long *) pmask); > + pmask[len >> 3] |=3D BIT(len & 7); > + len++; > } > } > return len - 1; > --=20 > 2.20.1 >=20 >=20 --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --9amGYk9869ThD9tj Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iF0EABECAB0WIQRPfPO7r0eAhk010v0w5/Bqldv68gUCXjQkOgAKCRAw5/Bqldv6 8sEXAKDEBaLFMfGhZMoUFbXvMi75isxPaQCePgdIxpXSVK7wV2W2gywre2XfJso= =7k6g -----END PGP SIGNATURE----- --9amGYk9869ThD9tj--