From owner-freebsd-amd64@FreeBSD.ORG Wed Feb 12 22:19:44 2014 Return-Path: Delivered-To: freebsd-amd64@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id D9FDFC92 for ; Wed, 12 Feb 2014 22:19:44 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher ADH-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id AD3CB1519 for ; Wed, 12 Feb 2014 22:19:44 +0000 (UTC) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id D82E7B9A9; Wed, 12 Feb 2014 17:19:42 -0500 (EST) From: John Baldwin To: "Simon Matter" Subject: Re: amd64/186061: FreeBSD 10 crashes as KVM guest on GNU/Linux on AMD family 10h CPUs Date: Wed, 12 Feb 2014 17:18:26 -0500 User-Agent: KMail/1.13.5 (FreeBSD/8.4-CBSD-20130906; KDE/4.5.5; amd64; ; ) References: <201402120740.s1C7e1Mn005809@freefall.freebsd.org> <201402121423.48285.jhb@freebsd.org> <18f55baf8a13457d3d6a89fc4f4ffc61.squirrel@webmail.bi.corp.invoca.ch> In-Reply-To: <18f55baf8a13457d3d6a89fc4f4ffc61.squirrel@webmail.bi.corp.invoca.ch> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201402121718.26615.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Wed, 12 Feb 2014 17:19:42 -0500 (EST) Cc: freebsd-amd64@freebsd.org X-BeenThere: freebsd-amd64@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Porting FreeBSD to the AMD64 platform List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 12 Feb 2014 22:19:44 -0000 On Wednesday, February 12, 2014 4:04:53 pm Simon Matter wrote: > > On Wednesday, February 12, 2014 2:40:01 am Simon Matter wrote: > >> The following reply was made to PR amd64/186061; it has been noted by > >> GNATS. > >> > >> From: "Simon Matter" > >> To: bug-followup@FreeBSD.org > >> Cc: simon.matter@invoca.ch > >> Subject: Re: amd64/186061: FreeBSD 10 crashes as KVM guest on GNU/Linux > >> on > >> AMD family 10h CPUs > >> Date: Wed, 12 Feb 2014 08:30:51 +0100 > >> > >> ------=_20140212083051_97180 > >> Content-Type: text/plain; charset="iso-8859-1" > >> Content-Transfer-Encoding: 8bit > >> > >> As noted by John Baldwin the change to mca.c is not needed. Attached > >> patch > >> is what I'm using now with success. > >> > >> BTW: setting vm.pmap.pg_ps_enabled="0" in loader.conf does also > >> mitigate > >> the issue but I guess it's not the optimal solution. > > > > Talking with Alan Cox, we do think the right fix is to change the test to > > enable the workaround. However, we'd rather not penalize VM's on other > > I'm afraid that will not work in all situations, no matter how good the > tests are (see below why I think so). So as a last resort, I suggest that > it should be possible to enable the "AMD Erratum 383" workaround via > loader.conf. I think you misunderstand. We would only use flags that are never set on an AMD 10h CPU, so they can never be set in a KVM guest that would ever migrate to an AMD 10h CPU. If those flags are present, we know that we would _not_ need the workaround. If none of those flags are present, we would enable the workaround. Does that make sense? -- John Baldwin