FSGSBASE Testing Is Encouraged Ahead Of Linux 5.9

[ezst036]

Is it true this also speeds up AMD CPUs?

For anybody who knows, what would be the earliest processor family that might benefit from this? Bulldozer? K10h?(phenom II, etc)

[Space Heater]

what would be the earliest processor family that might benefit from this?

It would appear that 15h and newer support FSGSBASE, so that is Bulldozer and newer. I'm not sure if 16h (Jaguar/Puma) support it though.

Source: AMD's BIOS and Kernel Developer’s Guide. (page 32, under "Architectural changes")

[ezst036]

Thank you.

[V1tol]

Another one stupid question - if I use "mitigations=off" will performance change at all with this patch?

[Space Heater]

FSGSBASE patches seem to have issues with host systems running VMs through VirtualBox on Ryzen processors. I had to remove FSGSBASE patches from Zen Kernel after a report that a 3950x user was getting stalls and freezes after the patches were added: https://github.com/zen-kernel/zen-kernel/issues/172

I saw in the bug report another user reported system freezes with qemu/kvm virtual machines and FSGSBASE.

On 5.8-rc2 with FSGSBASE patches, I've run a Windows vm via qemu/kvm for over 12 hours now and so far I've experienced no hangs or oops messages.