I'm trying to install CentOS 7 using Hyper-V and it's failing with the following error message:
tsc: Fast TSC calibration failed
PCI: Fatal: No config space access function found
i8042: No controller found
[long waiting period...]
dracut-initqueue[475]: Warning: Could not boot.
dracut-initqueue[475]: Warning: /dev/disk/by-label/CentOS-7-livecd-x86_64 does not exist
dracut-initqueue[475]: Warning /dev/mapper/live-rw does not exist
Warning: /dev/disk/by-label/CentOS-7-livecd-x86_64 does not exist
Warning: /dev/mapper/live-rw does not exist
Generating "/run/initramfs/rdsosreport.txt"
I have created a Generation 2 virtual machine and disabled Secure Boot so it would at least start booting.
CentOS 7 currently does not support running on Hyper-V Generation 2 virtual machines, as can be seen here. You have to recreate the VM and specify Generation 1 as the VM type.
Linux Virtual Machines on Hyper-V provides a comprehensive list of which distributions are supported and any limitations associated with them.
For a list of the differences between Gen1 and Gen2 virtual machine, check this page. You'll notice Legacy BIOS is gone in favor of UEFI.
You don't need to switch back to a Generation 1 virtual machine. You can use a Generation 2 virtual machine, so long as you disable Secure Boot.
To quote from Microsoft:
Supporting Secure Boot is still a work-in-progress in most Linux distributions.
I suspect more recent versions of CentOS will eventually no longer have the issue you faced (see https://bugzilla.redhat.com/show_bug.cgi?id=1192030 for the same issue in Fedora)