[mywittyname]

The 360 has a Type 1 (bare metal) hypervisor. So there's not much, if any, performance impact to having it since the software runs natively on the hardware.

Microsoft used a hypervisor primarily for security. They wanted to ensure that only signed code could be executed and wanted to prevent an exploit in a game from allowing the execution of unsigned code with kernel privileges on the system itself.

Every ounce of performance lost to the hypervisor is money Microsoft wasted in hardware costs. So they had an incentive to make the HyperV as performant as possible.

[dijit]

the 360 has no hypervisor.

The CPU had an emulator that you could run on x86 Windows, but it was not itself a hypervisor.

The hypervisor in the XB1 served a more important purpose: to provide developers a way of shipping the custom SDK to clients, and not forcing them to update it. This was quite important for software stability and in fact we made a few patches to MS's XB1 SDK (Durango) to optimise it for our games.

VM's are VM's, there are performance trade-offs.

I know this because I worked on AAA games before in this area, do you also work in games and are repeating something you think. you heard?

[mywittyname]

I don't work in the industry. But just because you "worked on AA games" before doesn't make you correct.

This detailed architectural overview of the 360 discusses the hypervisor:

https://www.copetti.org/writings/consoles/xbox-360/

This YouTuber, who is an industry vet, and has done several xbox ports claims the XB360 has a hypervisor:

https://www.youtube.com/watch?v=Vq1lxeg_gNs

And there entries in the CVE database for the XB360 which describe the ability to run code in "hypervisor mode":

https://www.cvedetails.com/cve/CVE-2007-1221/

This detailed article on the above exploit goes into detail on how the memory model works on the XB360, including how main memory addressing works differently in hypervisor mode than in real mode:

https://www.360-hq.com/article1435.html

That's a whole lot of really smart people discussing a topic that you claim doesn't exist.

[dijit]

Appreciate the detailed reply!

> This detailed architectural overview of the 360 discusses the hypervisor:

> https://www.copetti.org/writings/consoles/xbox-360/

Yes, the 128KB of key storage and W^X. That's not a hypervisor in the sense that the XB1/HyperV or VMWare have a hypervisor, they shouldn't even share a name it's not the same thing at all.

It's like calling the JVM is a virtual machine in the same way QEMU is.

The 360 "Hypervisor" is more akin to a software T2 chip than anything that actually virtualises.

[robocat]

I don’t think you are showing respect when you simplistically repeat your assertion without effort, after two people expended their precious time to tell you in detail that you are wrong with examples. I don’t know anything, but a few minutes following the provided links and I find https://cxsecurity.com/issue/WLB-2007030065 which says:

  The Xbox 360 security system is designed around a hypervisor concept. All games and other applications, which must be cryptographically signed with Microsoft's private key, run in non-privileged mode, while only a small hypervisor runs in privileged ("hypervisor") mode. The hypervisor controls access to memory and provides encryption and decryption services.

  The policy implemented in the hypervisor forces all executable code to be read-only and encrypted. Therefore, unprivileged code cannot change executable code. A physical memory attack could modify code; however, code memory is encrypted with a unique per-session key, making meaningful modification of code memory in a broadly distributable fashion difficult. In addition, the stack and heap are always marked as non-executable, and therefore data loaded there can never be jumped to by unpriviledged code.

  Unprivileged code interacts with the hypervisor via the "sc" ("syscall") instruction, which causes the machine to enter hypervisor mode.

You can argue your own definition of what a hypervisor is, but I suspect you won’t get any respect for doing so.

[black3r]

360 indeed uses hypervisor [0], but uses it only for security, to make the app signature verification run on a higher level.

Windows on PCs also runs under hypervisor if you enable some security features (e.g. VBS/HVCI which are on by default since Windows 11 2022 update, or Windows Sandbox, or WDAG) or enable Hyper-V itself (e.g. to use WSL2/Docker).

The performance losses are indeed there, but by purely running the hypervisor you lose just around 1% [1], because the only overhead is added latency due to accessing memory through SLAT and accessing devices through IOMMU...

I'd imagine XB1 is running with all the security stuff enabled though, which demands additional performance losses [2]..

[0]: https://www.engadget.com/2005-11-29-the-hypervisor-and-its-i...

[1]: https://linustechtips.com/topic/1022616-the-real-world-impac...

[2]: https://www.tomshardware.com/news/windows-11-gaming-benchmar...