Re: [PATCH] KVM: x86: enable TDP MMU by default

[Paolo Bonzini]

On 7/26/22 16:57, Stoiko Ivanov wrote:
> Hi,
>
> Proxmox[0] recently switched to the 5.15 kernel series (based on the one
> for Ubuntu 22.04), which includes this commit.
> While it's working well on most installations, we have a few users who
> reported that some of their guests shutdown with
> `KVM: entry failed, hardware error 0x80000021` being logged under certain
> conditions and environments[1]:
> * The issue is not deterministically reproducible, and only happens
>    eventually with certain loads (e.g. we have only one system in our
>    office which exhibits the issue - and this only by repeatedly installing
>    Windows 2k22 ~ one out of 10 installs will cause the guest-crash)
> * While most reports are referring to (newer) Windows guests, some users
>    run into the issue with Linux VMs as well
> * The affected systems are from a quite wide range - our affected machine
>    is an old IvyBridge Xeon with outdated BIOS (an equivalent system with
>    the latest available BIOS is not affected), but we have
>    reports of all kind of Intel CPUs (up to an i5-12400). It seems AMD CPUs
>    are not affected.
>
> Disabling tdp_mmu seems to mitigate the issue, but I still thought you
> might want to know that in some cases tdp_mmu causes problems, or that you
> even might have an idea of how to fix the issue without explicitly
> disabling tdp_mmu?

If you don't need secure boot, you can try disabling SMM.  It should not 
be related to TDP MMU, but the logs (thanks!) point at an SMM entry (RIP 
= 0x8000, CS base=0x7ffc2000).

This is likely to be fixed by 
https://lore.kernel.org/kvm/20220621150902.46126-1-mlevitsk@xxxxxxxxxx/.

Paolo