[Qemu-devel] [Bug 1715700] Re: Windows 7 guest won't boot on qemu 2.10 (works on 2.9)

[Laszlo Ersek \(Red Hat\)]

I'd also like to mention that, when we originally worked on the VBE
Shim, I tried to put it elsewhere. Obviously it has to be pointed-to by
a real mode interrupt vector, which limits quite a bit where it can go
at all; the point is that I tried to put it into low *RAM* (under
640KB).

It didn't work. Windows 7 would only accept the VBE Shim when it existed
in the C segment, i.e. where a VGA option ROM would normally be located.

This is just to say that moving the VBE Shim out of the C segment (into
real-mode addressible RAM) will not work.

The symptom described in the original report is likely due to

- Windows following the 0x10 interrupt vector (from page 0) to the C
segment,

- copying a bunch of zeros into its real mode emulator from the C
segment (where now no actual VBE code can be found),

- and then seeing no results when the real mode emulator executes the
zeros.

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https://bugs.launchpad.net/bugs/1715700

Title:
  Windows 7 guest won't boot on qemu 2.10 (works on 2.9)

Status in QEMU:
  New

Bug description:
  Qemu version: 2.10 stable.
  Guest: Windows 7 SP1 x64, virtio drivers are already installed in the guest.
  Command line:
  qemu-system-x86_64 \
      -nodefaults \
      -nodefconfig \
      -machine type=q35,accel=kvm \
      -enable-kvm \
      -cpu host \
      -m 2048 \
      -vga virtio \
      -boot menu=on \
      -smbios file=/path/dmidecode_BIOS.bin \
      -acpitable file=/path/acpi_slic.bin \
      -bios /path/OVMF_CODE.fd \
      -net none \
      -drive if=virtio,media=disk,file=/media/win7.qcow2 \
      -device pcie-root-port \
      -device ich9-usb-ehci1 \
      -device ich9-usb-uhci1 \
      -device ich9-usb-uhci2 \
      -device ich9-usb-uhci3

  Windows hangs at boot with waving flag screen (flag doesn't freeze,
  keeps waving indefinitely). Same command line boots fine with Qemu
  2.9. I tried changing machine type to pc-q35-2.9 - same result.

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