Live migration regarding Intel PT

[Xiaoyao Li]

Hi Eduardo,

I have some question regrading Intel PT live migration.

Commit "e37a5c7fa459 (i386: Add Intel Processor Trace feature support)" 
expose Intel PT with a fixed capabilities of CPUID 0x14 for live 
migration. And the fixed capabilities are the value reported on 
ICX(IceLake). However, the upcoming SPR(Sapphire Rapids) has less 
capabilities of INTEL_PT_CYCLE_BITMAP than ICX. It fails to enable PT in 
guest on SPR machine.

If change the check on INTEL_PT_CYCLE_BITMAP to allow different value to 
allow it work on SPR. I think it breaks live migration, right?

For me, not making each sub-function of PT as configurable in QEMU 
indeed makes it hard for live migration. Why not make PT as unmigratable 
in the first place when introducing the support in QEMU?

Thanks,
-Xiaoyao