Flags to turn off Hyper-V IPI & TLB flush enlightenment?

[verulian]

I've been having trouble with BSODs in Windows 10 virtual machines that are apparently, according to VirtIO driver developers where they've seen an ENORMOUS number of such crashes, due to needing to disable Hyper-V IPI and TLB flush enlightenment. There are, it appears, flags that can disable these, but I'm not finding them with Proxmox. Are these available somewhere/somehow?

 

[spirit]

Hi, hv-ipi && hv-tlbflush are not enabled by default in proxmox. (you can check the generated kvm commande line with a "ps -aux")

 

[verulian]

Hmm, unfortunately I do see the following in the `-cpu` arguments for the guest VM in question:

-cpu kvm64,enforce,hv_ipi,hv_relaxed,hv_reset,hv_runtime,hv_spinlocks=0x1fff,hv_stimer,hv_synic,hv_time,hv_vapic,hv_vpindex,+kvm_pv_eoi,+kvm_pv_unhalt,+lahf_lm,+sep

Does this mean I should somehow disable hv_ipi and/or does this have bearing on hv-tlbflush (hv_tlbflush)?

 

[spirit]

Hmm, unfortunately I do see the following in the `-cpu` arguments for the guest VM in question:

-cpu kvm64,enforce,hv_ipi,hv_relaxed,hv_reset,hv_runtime,hv_spinlocks=0x1fff,hv_stimer,hv_synic,hv_time,hv_vapic,hv_vpindex,+kvm_pv_eoi,+kvm_pv_unhalt,+lahf_lm,+sep

Does this mean I should somehow disable hv_ipi and/or does this have bearing on hv-tlbflush (hv_tlbflush)?

oh, sorry, hv_ipi is enabled by default for win >=7 indeed, bu not hv-tlbflush.

I don't think that it's possible to disable hv_ipi, until you hack

/usr/share/perl5/PVE/QemuServer/CPUConfig.pm

to remove

        if (min_version($machine_version, 3, 1)) {
            $flagfn->('hv_ipi', undef, $win7_reason);
        }

 

[verulian]

What are the ramifications, if any, of hacking the CPU configurator to do this?

And is there a reason this isn't a standard function/option yet if Redhat/VirtIO are seeing so many problems?

 

[spirit]

What are the ramifications, if any, of hacking the CPU configurator to do this?

And is there a reason this isn't a standard function/option yet if Redhat/VirtIO are seeing so many problems?

because it's not implement in proxmox "cpuflags:" tunable option currently.(the list of tunable flag is specific).

BTW, do you have some reference of hv-ipi bug. (I'm running a lof of win2019 server (+-200), I never had a single crash).

I'm aware about tbl-flush potential bug, that's why it's not enabled by defualt.