[Bug 1811533] Re: Unstable Win10 guest with qemu 3.1 + huge pages + hv_stimer

[Heiko Sieger]

Also affects me when running Qemu 4.0.0 with -machine pc-q35-3.1. I get
this on the command line:

"qemu-system-x86_64: vhost_region_add_section: Overlapping but not
coherent sections at 11a000".

h/w: AMD Ryzen 3900X, Gigabyte Aorus Pro X570 (latest BIOS), kernel
5.3.0.

With -machine q35 (i.e. pc-q35-4.0) the machine crashes when soundhw is
specified. Here the quick and dirty command line:

qemu-system-x86_64 \
  -enable-kvm \
  -runas user \
  -serial none \
  -parallel none \
  -nodefaults \
  -name $vmname,process=$vmname \
  -machine pc-q35-3.1,accel=kvm,mem-merge=off,vmport=off \
-cpu 
host,kvm=off,+topoext,hv_vendor_id=1234567890ab,hv_vapic,hv_time,hv_relaxed,hv_spinlocks=0x1fff,hv_crash,hv_reset,hv_vpindex,hv_runtime,hv_synic,hv_stimer
 \
  -smp 24,sockets=1,cores=12,threads=2 \
    -global ICH9-LPC.disable_s3=1 \
    -global ICH9-LPC.disable_s4=1 \
  -m 48G \
-mem-path /dev/hugepages \
-mem-prealloc \
  -rtc base=localtime,clock=host,driftfix=slew  \
-soundhw hda \
-audiodev pa,id=pa1,server=/run/user/1000/pulse/native \
  -vga none \
  -nographic \
-usb \
-device usb-host,vendorid=0x046d,productid=0xc52b \
-device ioh3420,id=root_port1,chassis=1,bus=pcie.0,addr=03.0 \
-device 
vfio-pci,host=0b:00.0,id=hostdev1,bus=root_port1,addr=0x00,multifunction=on \
-device vfio-pci,host=0b:00.1,id=hostdev2,bus=root_port1,addr=0x00.1 \
  -drive if=pflash,format=raw,readonly,file=/usr/share/OVMF/OVMF_CODE.fd \
  -drive if=pflash,format=raw,file=/tmp/my_vars.fd \
...

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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

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