On Fri, May 17, 2024 at 8:18 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> > Ok, so it does look like a CPU issue. Even with the fixes you identified, I
> > don't see any other solution than adding scary text in Kconfig, defaulting
> > it to "n", and adding an also-very-scary pr_err_once("...") the first time
> > VMPTRLD is executed with CONFIG_KVM_INTEL_PROVE_VE.
>
> I don't think we need to make it super scary, at least not yet. KVM just needs
> to not kill the VM, which thanks to the BUSY flag is trivial: just resume the guest.
> Then the failure is "just" a WARN, which won't be anywhere near as problematic for
> KVM developers.
>
> If we don't have a resolution by rc6 or so, then maybe consider doing something
> more drastic?
>
> I agree that it should be off by default though. And the help text should be
> more clear that this intended only for developers and testing environments.
>
> I have a handful of patches, including one to not kill the VM. I'll try to post
> them later today, mostly just need to write changelogs.
>
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 75082c4a9ac4..5c22186671e9 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -98,15 +98,15 @@ config KVM_INTEL
>
> config KVM_INTEL_PROVE_VE
> bool "Check that guests do not receive #VE exceptions"
> - default KVM_PROVE_MMU || DEBUG_KERNEL
> - depends on KVM_INTEL
> + depends on KVM_INTEL && KVM_PROVE_MMU
> help
"depends on KVM_PROVE_MMU" is wrong, I think. I'd like to keep it
enabled without slowing down too much the VMs, for example.
On the other hand "default DEBUG_KERNEL" is definitely too heavy
with these CPU issues.
Paolo
