On Thu, 18 Aug 2022, Ben Hutchings wrote:
I suspect someone thought it would be a good idea to compile the kernel for P4 only, as both PIII and Athlon XP processors lack the SSE2 instruction set.That was a good guess, though we don't change the configuration like that in stable updates.
Well, that happened for Firefox, it became SSE2 only when they switched to a higher upstream version in a stable update. 78.15.0esr-1~deb11u1 is the last version that works on non SSE2 CPUs.
The RETbleed mitigations, which are not needed on these CPUs or even functional on 32-bit kernels, interact with the Spectre v2 mitigations, which *are* used on these CPUs. And unfortunately the RETbleed mitigations added some unconditional LFENCE instructions, which should be conditional since they are part of SSE2. As a temporary workaround, disabling the Spectre v2 mitigation with the kernel parameter "nospectre_v2" should allow this kernel version to run on older CPUs without SSE2. We'll fix this properly in a later update.
Glad to know that was just a mistake. I will stay with 5.10.0-16 until the next update shows up. -- Etienne Vogt (Etienne.Vogt@obspm.fr) Observatoire de Paris-Meudon Service Informatique