Windows 8, Fedora 19 OS Hyper-V Virtual Machine

Open a Terminal (Ctrl-Alt-T)
Run
```
  sudo vi /etc/default/grub 
```
Find the line starting with GRUB_CMDLINE_LINUX, and add
```
  video=hyperv_fb:[the resolution you want]
```

If the resolution I want is 1280×720 then my line ends up looking like this:

    GRUB_CMDLINE_LINUX="… quiet splash video=hyperv_fb:1280×720"

Run:

  sudo grub2-mkconfig -o /boot/grub2/grub.cfg

or when installed in EFI mode

  sudo grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg

(Note: this is just an over-sized reply.)

I'm using Windows 10 and Fedora 26. Basically what Daniel said still holds, with some modifications:

The file /boot/grub2/grub.cfg doesn't exist on fresh install Fedora 26, and creating the file doesn't affect booting parameters at all (verified with /proc/cmdline). The correct file is /boot/efi/EFI/fedora/grub.cfg (I get the path from Fedora Wiki).
Not every resolution is supported: 1920x1080 is, 2560x1080 is not. Unsupported resolution is simply ignored. I ended up setting it 1920 although my monitor is 2560.

And finally an advice: back up everything you edit. You'll need it some day.

Update: still works in Fedora 27.

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