2016-08-15 13:19+0800, Wanpeng Li: > 2016-08-12 19:39 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >> 2016-08-12 18:14+0800, Wanpeng Li: >>> 2016-08-12 17:44 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >>>> 2016-08-12 14:07+0800, Wanpeng Li: >>>>> 2016-08-09 2:16 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >>>>>> If vmcs12 does not intercept APIC_BASE writes, then KVM will handle the >>>>>> write with vmcs02 as the current VMCS. >>>>>> This will incorrectly apply modifications intended for vmcs01 to vmcs02 >>>>>> and L2 can use it to gain access to L0's x2APIC registers by disabling >>>>>> virtualized x2APIC while using msr bitmap that assumes enabled. >>>>>> >>>>>> Postpone execution of vmx_set_virtual_x2apic_mode until vmcs01 is the >>>>>> current VMCS. An alternative solution would temporarily make vmcs01 the >>>>>> current VMCS, but it requires more care. >>>>> >>>>> There is a scenario both L1 and L2 are running on x2apic mode, L1 >>>>> don't own the APIC_BASE writes, then L2 is intended to disable x2apic >>>>> mode, however, your logic will also disable x2apic mode for L1. >>>> >>>> You mean a case where L1 does intercept APIC_BASE? >>>> >>>> That case is not affected, because it should cause a nested VM exit, so >>>> vmx_set_virtual_x2apic_mode() won't be called in the first place. >>> >>> I mean L1 doesn't intercept APIC_BASE. >> >> Then L2's write to APIC_BASE should only affect L1. >> L2 is buggy if it intended to disable its x2APIC with the write >> or L1 set up intercepts incorrectly for the indented L2. > > Do you mean OS disable x2APIC during its running is buggy? Not in general, but if L1 doesn't intercept APIC_BASE and L2 writes to it in order to disable its (L2's) x2APIC, then there is a bug in L2 or L1. If L1 intended to intercept, then it's a clear L1 bug, otherwise L2 should have known that L1 is a special hypervisor that doesn't intercept APIC_BASE and the bug is on L2 side or on the user that ran unsuspecting L2 on that L1. -- 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
