Date: Wed, 12 Feb 2014 17:18:26 -0500 From: John Baldwin <jhb@freebsd.org> To: "Simon Matter" <simon.matter@invoca.ch> Cc: freebsd-amd64@freebsd.org Subject: Re: amd64/186061: FreeBSD 10 crashes as KVM guest on GNU/Linux on AMD family 10h CPUs Message-ID: <201402121718.26615.jhb@freebsd.org> In-Reply-To: <18f55baf8a13457d3d6a89fc4f4ffc61.squirrel@webmail.bi.corp.invoca.ch> References: <201402120740.s1C7e1Mn005809@freefall.freebsd.org> <201402121423.48285.jhb@freebsd.org> <18f55baf8a13457d3d6a89fc4f4ffc61.squirrel@webmail.bi.corp.invoca.ch>
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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" <simon.matter@invoca.ch> > >> 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
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