On Wed, Jan 31, 2018 at 02:04:49PM +0000, Dr. David Alan Gilbert wrote: > * Borislav Petkov (bp@xxxxxxx) wrote: > > On Wed, Jan 31, 2018 at 12:30:36PM +0000, Dr. David Alan Gilbert wrote: > > > Indeed, it's only for this weird case where you suddenly need to change > > > it. > > > > No, there's more: > > > > .name = "Broadwell-noTSX", > > .name = "Haswell-noTSX", > > Haswell came out and we made the CPU definition, and then got a > microcode update that removed the feature. > > So the common feature of noTSX and IBRS is that they're the only two > cases where a CPU has released and then the flags have changed later. Also, if anybody don't like it, users can already specify, e.g., "Broadwell,-hle,-rtm" or "Skylake,+spec_ctrl". QEMU only adds have the -noTSX and -IBRS CPU for convenience of management systems that don't know how to check/configure individual CPU features. We're working with libvirt and OpenStack folks to make this kind of trick unnecessary. -- Eduardo
