On Wed, Aug 01, 2018 at 11:27:26AM -0400, Bryan Steele wrote: > On Wed, Aug 01, 2018 at 03:46:25PM +0200, Elmer Skjødt Henriksen wrote: > > After installing the 014_amdlfence patch released yesterday for 6.3, my > > OpenBSD VM crashes on boot. It's running under KVM on a Linux box (Ubuntu > > 18.04 w/ kernel 4.15) on an AMD Ryzen 7 1700 (microcode 0x8001137). > > I suppose this would also happen on vmm(4) and bhyve, however I don't have > > any such AMD hosts available for testing. > > Hi Elmer, > > This was tested in vmm(4), which does work, unfortunately there was not > extensive testing by in other virtualization software. The MSR that is > being set here is only mentioned in AMDs whitepaper and I had no reason > to believe any special consideration was needed for guest VMs on AMD > processors. > > > It occurs both using libvirt's "EPYC" CPU model and using "host-passthrough" > > (i.e. no virtual CPU model), but the "core2duo" CPU model works fine. > > > > I guess not many people are running OpenBSD as a VM, and even less on AMD > > hardware. But still, a syspatch leaving the system unable to boot is > > probably not a good thing. :) > > > > Even so, I would like to apologize. This situation is unfortunate, and > I'll try to work with other developers to find the best way forward. > But, I regret I am only but an amateur magician. > > -Bryan.
Actually, it looks like this is at least partially a KVM/QEMU bug. In the meantime I guess the solution would be to do as you suggested and set a different CPU model for now until Linux distros include a fix for this. https://lkml.org/lkml/2018/2/21/1202 Afterwards, on the OpenBSD side, it looks like one small change may be required in addition.. -Bryan. Index: sys/arch/amd64/amd64/identcpu.c =================================================================== RCS file: /cvs/src/sys/arch/amd64/amd64/identcpu.c,v retrieving revision 1.95.2.2 diff -u -p -u -r1.95.2.2 identcpu.c --- sys/arch/amd64/amd64/identcpu.c 30 Jul 2018 14:45:05 -0000 1.95.2.2 +++ sys/arch/amd64/amd64/identcpu.c 1 Aug 2018 16:09:50 -0000 @@ -650,8 +650,10 @@ identifycpu(struct cpu_info *ci) msr = rdmsr(MSR_DE_CFG); #define DE_CFG_SERIALIZE_LFENCE (1 << 1) - msr |= DE_CFG_SERIALIZE_LFENCE; - wrmsr(MSR_DE_CFG, msr); + if ((msr & DE_CFG_SERIALIZE_LFENCE) == 0) { + msr |= DE_CFG_SERIALIZE_LFENCE; + wrmsr(MSR_DE_CFG, msr); + } } }
