[vfio-users] Stuttering in VM and "ignored rdmsr: 0x122" on new kernels?

[Bronek Kozicki]

Thank you, that helped!

I checked that 0x122 corresponds with a new MSR introduced by Intel to disable TSX, called MSR_IA32_TSX_CTRL . I have also found that in kernel 5.5 there's been a series of changes to hard-disable TSX inside KVM guests with MSR_IA32_TSX_CTRL (merged to mainline in 752272f16dd18f2cac58a583a8673c8e2fb93abb )

The funny thing is that my CPU is Ivy Bridge, i.e. the last generation *before* addition of TSX. Perhaps KVM does not check it, or perhaps it's my fault for using a relatively new microcode patch which somehow fools the kernel. Or perhaps the problem is elsewhere. Anyways, switching this option seem to have fixed the problem!


B.

On Sat, 31 Oct 2020, at 6:32 PM, sL1pKn07 SpinFlo wrote:
> El vie., 30 oct. 2020 a las 23:56, Bronek Kozicki
> (<brok at incorrekt.com>) escribió:
> >
> > I recently tried upgrading from vanilla LTS kernel 5.4 to vanilla 5.8 and found that my virtual machines "stutter" when they did not previously. The hypervisor is configured with tickless kernel (NO_HZ_FULL) and physical cores are exclusively reserved for vcpus by means of isolcpus , nohz_full and rcu_nocbs. The user experience under kernel 5.4 is good, it's only 5.8 when stuttering happens. This could be either just a brief "pop" when playing music, every few seconds, or actual short screen-freeze when playing games under Windows VM (I use GPU pass-through with Nvidia Quadro cards).
> >
> > This seem to correspond with messages appearing on hypervisor console which look like:
> >
> > [41426.188902] kvm [176116]: vcpu10, guest rIP: 0x7ff87a6a2aba ignored rdmsr: 0x122
> > [41426.202067] kvm [176116]: vcpu10, guest rIP: 0x7ff87a6a2aba ignored rdmsr: 0x122
> > [41426.218588] kvm [176116]: vcpu10, guest rIP: 0x7ff87b6d1d3a ignored rdmsr: 0x122
> > [41451.754213] kvm [1644425]: vcpu3, guest rIP: 0x7f5d4b442335 ignored rdmsr: 0x122
> > [41482.036754] kvm [176116]: vcpu2, guest rIP: 0x76f320ea ignored rdmsr: 0x122
> > [41482.181285] kvm [176116]: vcpu2, guest rIP: 0x76f320ea ignored rdmsr: 0x122
> > [41482.188947] kvm [176116]: vcpu2, guest rIP: 0x76d27f55 ignored rdmsr: 0x122
> >
> > There is quite a lot of it, but only logged by kernel 5.8 and not by 5.4 (I skipped 5.5 , 5.6 and 5.7).
[ cut ]

> 
> try with
> 
> └───╼  cat /etc/modprobe.d/kvm.conf
> options kvm ignore_msrs=0
> 
> greetings
>

-- 
  Bronek Kozicki
  brok at incorrekt.com