Hi Dave, On 6/6/25 07:29, Dr. David Alan Gilbert wrote: > * Babu Moger (babu.mo...@amd.com) wrote: >> Add CPUID bit indicates that a WRMSR to MSR_FS_BASE, MSR_GS_BASE, or >> MSR_KERNEL_GS_BASE is non-serializing amd PREFETCHI that the indicates >> support for IC prefetch. >> >> CPUID_Fn80000021_EAX >> Bit Feature description >> 20 Indicates support for IC prefetch. >> 1 FsGsKernelGsBaseNonSerializing. > > I'm curious about this: > a) Is this new CPUs are non-serialising on that write? > b) If so, what happens if you run existing kernels/firmware on them? > c) Bonus migration question; what happens if you live migrate from a host > that claims to be serialising to one that has the extra non-serialising > flag but is disabled in the emulated CPU model.
Good question. After looking at the AMD64 Architecture Programmer’s Manual again, these writes have always been non-serializing. Behavior has not changed. We're just reporting it through CPUID now. This information likely isn’t being used anywhere. Let me know if you have any questions. -- Thanks Babu Moger
