Acer Predator Helios 16 (PH16-71). Has anyone had any luck undervolting?

Using grubx64.efi’s setup_var option I managed to alter the following registers in CpuSetup:

CFG Lock (0x43)
Overclocking Lock (0x10E)
Undervolt Protection (0x381)

You can do all of this in the hidden BIOS menu (accessible via Smokeless Runtime EFI Patcher), as well, although CFG Lock goes under a different name there, it is what handles PL1/PL2 toggling.

I DO have access to PL1/PL2 limit changing---the CPU can run at about 155-160W now, technically it can do anything I want it to, but, well, pesky temperatures.

Which leads us to... undervolting. Undervolt Protection does NOT do anything. On or off, can't undervolt. More curious is that the hidden BIOS menu has undervolting options! Although it doesn't matter what you put in them, as they will never apply either.

Curiously however, they save between reboots. So it's saving a setting it doesn't care to apply?

My strongest lead thus far is that there seems to be an issue on boot where DXE or PEI is NOT sending the value (of the undervolt (if you apply it via BIOS) OR the okay to BE undervolted (whether by BIOS or ThrottleStop/etc.) once in runtime) to the CPU via IA32_OC_MAILBOX (MSR 0x150).

Even more curious, the laptop has no protection against OVERvolting. Yes, you can overvolt the CPU, which is ACTUALLY dangerous and harmful to it, but you cannot undervolt, which is wholly beneficial and has its most "dangerous" side effect being the inconvenience of a BSOD that you quickly recover from.

This is why I feel something can probably be done, because I feel if Acer was maliciously blocking out undervolting, overvolting would HAVE to be eliminated too (it's still the MSR 0x150 register), but I don't know what to do to enable it.

Overvolting is on the same MSR 0x150 IA32_OC_MAILBOX register! And it can actually be done. But for some reason, negative values (undervolting) do not work…

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DrSlowbro

I can also perform runtime overvolting via ThrottleStop. There's simply no block on overvolting, which implies that Acer merely didn't put in the allowance for undervolting like every other manufacturer (despite having the Undervolt Protection options…), as Intel's Plundervolt fix disallowed undervolting but not overvolting.

If there was any issue with MSR 0x150 IA32_OC_MAILBOX, it wouldn't be able to overvolt either, but it can. So I don't think Acer maliciously did anything to stop it, but they didn't do anything to allow it specifically either.

Again I'd really like to add that overvolting isn't even useful, this CPU will never under any circumstance benefit from it, it can only be harmed! But undervolting, even mildly, could improve CPU and temps by over 30%. That would be astronomical. And undervolting has literally 0 danger to it.

Sharanji

@DrSlowbro

It seems like you're onto something with the IA32_OC_MAILBOX register, but unfortunately, many users have reported that undervolting is locked out on the Predator Helios 16. Some have tried various methods, including accessing hidden BIOS menus, but haven't had much luck getting undervolting to apply.

Interestingly, there are reports that overvolting is still possible, which aligns with your findings. This suggests that Acer didn't explicitly block undervolting maliciously but rather didn't implement the necessary allowance for it.

Have you atempted unlocking additional BIOS settings using key combinations like Fn + Tab before booting, which supposedly reveals more options. However, it's unclear if this method works universally. ThrottleStop is often a go-to tool for undervolting, but if the CPU isn't accepting negative voltage values, it might require a deeper firmware-level modification. Check this conversation in this link
Overclocking/Undervoltage in predator helios neo 16 (PHN16-71-553K)Laptop

DrSlowbro

I've accessed the hidden BIOS menu. Fn+Tab doesn't work, but Smokeless Runtime EFI Patcher can allow it to load fine. There's nothing useful there as far as making undervolting work goes. Same options as grubx64.efi that I used, just easier to use since it's a GUI instead of command-line.

You can even "undervolt" in the hidden BIOS. I have a -150 mV undervolt (supposedly), but it never applies after I leave BIOS. Interestingly, this setting IS saving, I can check it right now and see it's still set to -150 mV, even though it never applies.

DrSlowbro

I was wondering if I could get any responses about this, Acer?

DrSlowbro

Some more findings. Maybe it can be of help to someone.

I saw an option under "Vulnerabilty Mitigation Mechanisms" in HWinfo64 called Dynamic Overclocking Undervolt Protection. Which is set to enabled. I see no option pertaining to this anywhere in my BIOS. So, the actual function for it goes under a different name, and at runtime it's presented as "Dynamic Overclocking Undervolt Protection".

I also made a full dump of my BIOS and used Intel's MFIT tool to skulk around for some other settings. I found some interesting stuff:

BIOS Guard Protection Override Enabled is set to No.
BIOS Guard seems to be a protection system of Intel's that verifies and cryptographically enforces BIOS updates, and prevents runtime BIOS region modification.

Unfortunately, this means BIOS modifications are out except for with an SPI flasher I think, unless someone managed to brute force the right cryptographic key, or something? I don't really know.

I don't understand why Acer made BIOS so utterly locked down that it has literally superficial Undervolt Protection options and even superficial undervolting options! But they ALLOW you to overvolt the CPU? That's literally DANGEROUS to the CPU and wholly pointless---no laptop CPU is going to hit such insanely high performance that it needs MORE voltage.