On Wed, 23 Feb 2022 09:16:51 +0000 "Dr. David Alan Gilbert" <dgilb...@redhat.com> wrote:
> * Igor Mammedov (imamm...@redhat.com) wrote: > > On Tue, 22 Feb 2022 10:42:55 +0100 > > Gerd Hoffmann <kra...@redhat.com> wrote: > > > > > Hi, > > > > > > > > And the upstream code is now pretty much identical except for the > > > > > default; note that for TCG you do need to keep to 40 I think. > > > > > > > > will TCG work with 40bits on host that supports less than that? > > > > > > When I understand things correctly the problem is that the phys-bits > > > limit applies to the npt/ept tables too, effectively restricting guest > > > physical address space to host physical address space. > > > > > > TCG is not affected by that and should work just fine. > > > > > > Not sure what happens if you turn off npt/ept and run on softmmu. > > > Possibly that works fine too. > > > > > > > Also quick look at host-phys-bits shows that it affects only 'host' > > > > cpu model and is NOP for all other models. > > > > > > I don't think so. microvm forces host-phys-bits=on and that works with > > > all cpu models. > > > > I just don't see how host-phys-bits can work for other than 'host' cpu > > model. > > It's true that property is available for all cpu models, but the field it > > sets > > is only used in target/i386/host-cpu.c, the same applies to > > host-phys-bits-limit. > > Am I missing something? > > The hook in kvm/kvm-cpu.c kvm_cpu_realizefn: > > /* > * The realize order is important, since x86_cpu_realize() checks if > * nothing else has been set by the user (or by accelerators) in > * cpu->ucode_rev and cpu->phys_bits, and updates the CPUID results in > * mwait.ecx. > * This accel realization code also assumes cpu features are already > expanded. > * > * realize order: > * > * x86_cpu_realize(): > * -> x86_cpu_expand_features() > * -> cpu_exec_realizefn(): > * -> accel_cpu_realizefn() > * kvm_cpu_realizefn() -> host_cpu_realizefn() > * -> check/update ucode_rev, phys_bits, mwait > */ Thanks, I didn't expect host_cpu_realizefn being called from elsewhere beside of cpu model it belongs to or models inherited from it. > > Dave > > > > > > > take care, > > > Gerd > > > > >
