From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Bader Subject: Re: [PATCH/RFC] Fix xsave bug on older Xen hypervisors Date: Fri, 07 Sep 2012 17:43:00 +0200 Message-ID: <504A1604.5030103@canonical.com> References: <1347018043-21252-1-git-send-email-stefan.bader@canonical.com> <504A05B00200007800099C7B@nat28.tlf.novell.com> <5049F4E9.9050306@canonical.com> <504A1A950200007800099D4C@nat28.tlf.novell.com> <20120907142251.GA20096@linuxtx.org> <20120907145433.GA5378@phenom.dumpdata.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============7317408952724608783==" Return-path: In-Reply-To: <20120907145433.GA5378@phenom.dumpdata.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --===============7317408952724608783== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="------------enigF04701155E33776907F5DA0F" This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigF04701155E33776907F5DA0F Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 07.09.2012 16:54, Konrad Rzeszutek Wilk wrote: >>> But iirc that bad patch is a Linux side one (i.e. you're trying to fi= x >>> something upstream that isn't upstream)? >>> >> Right, so the patch that this improves upon, and that Fedora and Ubunt= u are >> currently carrying is not upstream because: >> >> a) It's crap, it cripples upstream xen users, but doesn't impact RHEL = xen >> users because xsave was never supported there. >> >> b) The hypervisor was patched to make it unnecessary quite some time a= go, >> and we hoped EC2 would eventually pick up that correct patch and we co= uld >> drop the crap kernel patch. >> >> Unfortunately this has not happened. We are at a point where EC2 reall= y is >> a quirk that has to be worked around. Distros do not want to maintain >> a separate EC2 build of the kernel, so the easiest way is to cripple >> current upstream xen users. This quirk is unfortunately the best poss= ible >> solution. Having it upstream also makes it possible for any user to b= uild >> an upstream kernel that will run on EC2 without having to dig a random= >> patch out of a vendor kernel. >=20 > Sure. Jan is asking though for actual confirmation that the upstream ke= rnel > does indeed go belly up without a workaround. > And whether this patch (which I would did since Canonical is carrying i= t) does > fix the issue. It is really hard to tell. It might even be that all of the hosts on EC2 = are now upgraded. There might be different version around. Even back when the pro= blem was found it would not always happen. So it is, still a bit hackish, an attempt to play safe. All that is known= is that there happened to be hosts running Xen 3.something which would do th= at. Historical evidence might be: commit 389a3c02496dd1b399bb0efd005e9fa2be24e9ee Author: Jeremy Fitzhardinge Date: Tue Sep 18 22:46:33 2007 -0700 xen: don't bother trying to set cr4 Xen ignores all updates to cr4, and some versions will kill the domai= n if you try to change its value. Just ignore all changes. Of course this is ancient v2.6.23 and it was later relaxed to just filter= out some flags: commit 2956a3511c8c5dccb1d4739ead17c7c3c23a24b7 Author: Jeremy Fitzhardinge Date: Mon May 26 23:31:04 2008 +0100 xen: allow some cr4 updates The guest can legitimately change things like cr4.OSFXSR and OSXMMEXCPT, so let it. But whether there are still hosts out there running a bad version of the = HV is hard to say. EC2 may or may not be the only case (or not at all anymore).= For upstream Linux it would be a valid decision either way. Not adding a quir= k because the use-case is so small. Or adding it because it avoids special = patches in distros and forcing those bits off on Xen 3 hosts is an acceptable dra= wback. At least posting it here would allow those who carry the older more intru= sive hack to replace that. So we do not run again into that mess like when xsa= ve was half-disabled by guests with that patch and hosts supporting it. >=20 > I am still a newbie on the Amazon EC2 upload your kernel thing (hint, w= ould > appreciate somebody taking this patch and trying it out). >=20 > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel >=20 --------------enigF04701155E33776907F5DA0F Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://www.enigmail.net/ iQIcBAEBCgAGBQJQShYEAAoJEOhnXe7L7s6je7EP+wWVUwEZtLfe5lmf2UbhmbTW G0I1LxsrduIjDq1HiIlUsH733LGxWKOheg/jd6x/3D3i2+dhC8h8DIvzuEnZkaUQ iHUjmgiQAne/Qcm+qMtjtriVfNNqBw+MGCDu18Sk2JumMafxptrULTe7012VUJrd dPWpBrQlVbuT7b8oDoCSa+Sv2rJSIvu80k8Hsf5U1HND+Sy7xxhBSZYYQQ2/7Zvt 4Lg65Ldz7bD/9N25s1JStyVVP8wmJV4o3wFeNzDXHYdX96ADQA03/X+/tzEK3GhM ZUEtNtXudVE94YtMZkpu31mkRfDQEQeJfS3hWBBUfuRV42/N9wuoW59esLZgoE2H TI4GNjK+K0KTYdANx/QmlHh8Z4RTQPPeQEzkekJA84+wmDpq20p5VsEEWrgP7WF3 z4knzmPSA2vRrlWTUbR0UUmhoIvU//W1s+AiJqGUvpwLClnUlf55LG5FUBA05mV/ JPaSGR1U8Un9B+b4NRqKuleRvFPInqTJYWFJ0w/ngzq0DJm5RNdu1pK5Oj9Xr3mq aw4aGBprzlEaee3kZgRqFR8jy1epzFXszBDst4fnxWmz8TETGTaB4bQ8SMRp2mGi XvB7Kliv5G6PbBEUM7js+drjWFHRbgpsw7nFOFbXklATx0lCFkwGZSc+0oqgFrQT vAbZBpXUwAb0eH3ovA+Z =Wi7N -----END PGP SIGNATURE----- --------------enigF04701155E33776907F5DA0F-- --===============7317408952724608783== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel --===============7317408952724608783==--