Date: Wed, 10 Feb 2010 22:37:08 -0600 From: Alan Cox <alan.l.cox@gmail.com> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-stable@freebsd.org Subject: Re: Strange problem with 8-stable, VMWare vSphere 4 & AMD CPUs (unexpected shutdowns) Message-ID: <ca3526251002102037j21b11a7an572f397a9ae1eda0@mail.gmail.com> In-Reply-To: <20100210184623.GA78851@icarus.home.lan> References: <hkujop$hsa$1@ger.gmane.org> <4B72D94A.8030509@icyb.net.ua> <hkup1g$763$1@ger.gmane.org> <4B72E93C.80102@icyb.net.ua> <9bbcef731002101003r203f5189xf139700a0d48afa0@mail.gmail.com> <4B72F67F.4000209@icyb.net.ua> <9bbcef731002101026k5007075cqf97fc80404ac3fa7@mail.gmail.com> <4B72FC55.2090508@icyb.net.ua> <9bbcef731002101038r1ac04141t505216816489376f@mail.gmail.com> <20100210184623.GA78851@icarus.home.lan>
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On Wed, Feb 10, 2010 at 12:46 PM, Jeremy Chadwick <freebsd@jdc.parodius.com>wrote: [snip] > > I read what Andriy wrote to mean that the way FreeBSD utilises 4MB TLB > on certain models of AMD processors is broken/quirky, and on those CPUs, > users should stick to vm.pmap.pg_ps_enabled="0" (loader.conf). > > No. He said, "We don't do anything that strays from specifications." So, he is not saying that FreeBSD is doing anything broken. Here is what I know. Several of us, myself included, have been able to reproduce either lockups or machine check exceptions when BOTH the machine check driver and superpages are enabled on AMD family 10h processors. There have been no reports of this problem on either Intel or earlier AMD processors. Moreover, there is no evidence of instability in AMD family 10h processors until the machine check driver is enabled. By default, FreeBSD 8.0 enables superpages but disables the machine check driver. So, running natively, i.e., without virtualization, you shouldn't experience a problem, unless you explicitly enable the machine check driver. However, running on top of a hypervisor, like vSphere 4, you might face a problem because the hypervisor might enable machine check exceptions, regardless of what the FreeBSD guest does. I really don't know whether vSphere 4 enables machine check exception or not. If it does, then either you disable the use of superpages in the FreeBSD guest, or you find a way to disable the machine check driver in the hypervisor. Both Andriy and I have reported this problem to people at AMD, but we haven't yet received AMD's analysis. These things take time. Regards, Alan
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