Hacker News new | ask | show | jobs
by greglindahl 3465 days ago
If you have a more-recent-than-2014 kernel, BIOS, or stepping, the feature bit ought to be accurate.

So sure, there are some systems in the wild that are broken, but probably not that many.
1 comments
0x0 3465 days ago
Let's say you're deploying to a random cloud VM that may or may not have the latest microcode/BIOS. How do you know if TSX is safe to use? Can it be determined in software by looking at CPUID values? (If so, do all TSX-using libraries/compilers insert such checks?)

The risk of subtle locking bugs in multi threaded applications due to CPU bugs makes me want to shy away from the entire feature.

link
wtallis 3465 days ago
CPUID values would be sufficient. TSX should be correct on Haswell-EX (Xeon E7), Broadwell except for the tablet SoCs (Core M), and all Skaylake, Kaby Lake and newer.
link
greglindahl 3464 days ago
Note that most Linux distros put the latest microcode updates into all of their kernels for any supported version. That means that an updated box with an "old" distro is still going to be OK.
link
0x0 3464 days ago
Does that work under a hypervisor/xen/VM/whatever? Can you apply a microcode update only within a given VM?
link