On 4/23/2024 12:49 AM, David Woodhouse wrote: >> If I restored the KVM_REQ_GLOBAL_CLOCK_UPDATE request from >> kvm_arch_vcpu_load(), the selftest works for me, and I ran the test for >> 1000+ iterations, w/ or w/o TSC scaling, the TEST_ASSERT(delta_corrected >> <= ±1) never got hit. This is awesome! >> >> However, without KVM_REQ_GLOBAL_CLOCK_UPDATE, it still fails on creating >> a VM. Maybe the init sequence sill needs some rework. > > That one confuses me. The crash is actually in debugfs, as it's > registering the per-vm or per-vcpu stats. I can't imagine *how* that's > occurring. Or see why the availability of TSC scaling would cause it to > show up for you and not me. Can I have your .config please? > > First thought would be that there's some change in the KVM structures > and you have some stale object files using the old struct, but then I > realise I forgot to actually *remove* the now-unused > kvmclock_update_work from x86's struct kvm_arch anyway. > > I'll try to reproduce, as I think I want to *know* what's going on > here, even if I am going to drop that patch as mentioned in > https://lore.kernel.org/kvm/a6723ac9e0169839cb33e8022a47c2de213866ac.camel@xxxxxxxxxxxxx > > Are you able to load that vmlinux in gdb and > (gdb) list *start_creating+0x80 > (gdb) list *kvm_create_vm_debugfs+0x28b > > Thanks again. My apologies, it turns out the KVM_REQ_GLOBAL_CLOCK_UPDATE is not needed. Today I can't reproduce the issue after removing it. Yesterday I thought it may miss something related to pfncache. To be clear, with the above mentioned change to kvm_scale_tsc(master_tsc_scaling_ratio), the selftest runs reliably regardless TSC scaling is enabled or not.
