No, I think it's the other way around: clearing guest pages is unrelated. It is easy to check with the following kernel patch:
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index fff790a3f4ee..73c574f930e3 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -776,7 +776,7 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages) */ kvm_vcpu_deactivate_apicv(vcpu); synic->active = true; - synic->dont_zero_synic_pages = dont_zero_synic_pages; + synic->dont_zero_synic_pages = false; return 0; } my expectation is that the issue will remain. Now what *can* be causing it: when in-QEMU synic is initialized it creates two memory subregions: for Event page and for Message page (HV_X64_MSR_SIEFP/HV_X64_MSR_SIMP MSRs). These regions are always 4k in size and they can me anywhere in guest's memory, not necessarily 2M aligned. Now, (if I understood correctly) in vhost code, vhost_region_add_section() is trying to align to qemu_ram_pagesize() and this may intersect with synic regions. We need to summon someone who understands memory_region_* magic in QEMU and vhost in particular. -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1811533 Title: Unstable Win10 guest with qemu 3.1 + huge pages + hv_stimer Status in QEMU: Confirmed Bug description: Host: Gentoo linux x86_64, kernel 4.20.1 Qemu 3.1.0 CPU: Intel i7 6850K Chipset: X99 Guest: Windows 10 Pro 64bit (1809) Machine type: pc-q35_3.1 Hyper-V enlightenments: hv_stimer,hv_reenlightenment,hv_frequencies,hv_vapic,hv_reset,hv_synic,hv_runtime,hv_vpindex,hv_time,hv_relaxed,hv_spinlocks=0x1fff Memory: 16GB backed by 2MB huge pages Issue: Once guest is started, log gets flooded with: qemu-system-x86_64: vhost_region_add_section: Overlapping but not coherent sections at 103000 or qemu-system-x86_64: vhost_region_add_section:Section rounded to 0 prior to previous 1f000 (line endings change) and as time goes guest loses network access (virtio-net-pci) and general performance diminishes to extent of freezing applications. Observations: 1) problem disappears when hv_stimer is removed 2) problem disappears when memory backing with huge pages is disabled 3) problem disappears when machine type is downgraded to pc-q35_3.0 To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1811533/+subscriptions