AMD Preps BIOS Update to Fix FMA3 Freezes for Ryzen

AMD will be issueing a new BIOS for Ryzen motherboards, the company discovered why FMA3 code is causing system hangs on PCs using a new Ryzen desktop processor. AMD didn’t provide a detailed report on the root cause, the company said that BIOS changes will be distributed to motherboard manufacturers to resolve the issue. 

Customers are encouraged to keep an eye on their motherboard vendor’s website for an update, reports digital trends.

We are aware of select instances where FMA code can result in a system hang,” the company said. “We have identified the root cause.”

Ryzen processors reportedly cause a hard system lock when running certain FMA3 workloads. The first sign of trouble appeared in the open-source processor benchmark Flops (v2) by Alexander “Mystical” Yee. This simple program provides separate versions supporting specific processor architectures, such as Intel’s Haswell, Skylake, and so on. 

But because the author has yet to upload a version for AMD’s new Zen architecture used in the Ryzen chips, the Haswell-specific binary is the version of choice for testing Ryzen … at least, for now.

Using the Haswell binary is important because it supports the Fused Multiply-Add (FMA) microprocessor instruction set, which is also supported by AMD’s Ryzen processors. The short description of FMA is that the processor can compute A+BxC in one step before rounding the final result. The “unfused” method involves BxC first, rounding the number, adding that to A, and rounding the final result.

However, Ryzen’s issue with FMA3 isn’t locked to the Flops benchmark. Simple apps with basic user privileges can crash a Ryzen-based machine. Even more, code using FMA3 could be executed on virtual machines running on AMD’s upcoming Zen-based “Naples” processors for the enterprise. Thus, finding the FMA3 issue in Flops now saved AMD and corporations from a lot of headache stemming from the security implications alone at the launch of Naples.

“Don’t be fooled by the Haswell binary,” Yee said. “The benchmark is five years old and I’ve largely neglected it for the last three. So I haven’t updated it for Zen yet. Any processor will be able to run any of the binaries if it supports the underlying instruction sets. If it doesn’t, the program merely crashes with an ‘illegal instruction.’ Under no circumstances should a user-mode application be able to bring down an entire system.”