> No, both patches are wrong. Guys, thanks for looking into this bug. I'm afraid I'm still at a loss at why a TSC bug would even cause a guest lockup :( When Avi Kivity saw my nested TSC handling code he remarked "this is probably wrong". When I asked him where it was wrong, he basically said that he didn't know where, but TSC handling code is always wrong ;-) And it turns out he was right. > The correct fix is to make kvm_get_msr() return the L1 guest TSC at all times. > We are serving the L1 guest in this hypervisor, not the L2 guest, and so > should never read its TSC for any reason. ... > allows the L2 guest to overwrite the L1 guest TSC, which at first seems wrong, > but is in fact the correct virtualization of a security hole in the L1 guest. I think I'm beginning to see the error in my ways... When L1 lets L2 (using the MSR bitmap) direct read/write access to the TSC, it doesn't want L0 to be "clever" and give L2 its own separate TSC (like I do now), but rather gives it full control over L1's TSC - so reading or writing it should actually return L1's TSC, and the TSC_OFFSET in vmcs12 is to be ignored. So basically, if I understand correctly, what I need to change is in prepare_vmcs02(), if the MSR_IA32_TSC is on the MSR bitmap (read? write?), instead of doing vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset); I just need to do vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset); thereby giving L2 exactly the same TSC that L1 had. Brandan, if I remember correctly you once tried this sort of fix and it actually worked? Then, guest_read_tsc() will return (without need to change this code) the correct L1 TSC. And vmx_write_tsc_offset() should do in the is_guest_mode() not what it does now (vmcs12->tsc_offset is of no important when the TSC MSR is passed through) but rather set vmcs01_tsc_offset (which will be applied on the next exit to L1). Is my analysis correct? Or perhaps completely wrong? ;-) Am I missing anything else that should be change? In any case, I don't understand why on my machine I never encountered these problems, and nothing broke even if I replaced the TSC nesting code with randomly broken code. Are the people who are seeing this brakage actually passed the MSR from L1 to L2 - using the MSR bitmap - like I guessed above? Or am I missing something completely different? Sorry, but I'm really becoming confused by these TSC issues... Thanks, Nadav. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html