Messages in this thread | | | Date | Wed, 10 Nov 2021 16:01:49 +0100 | Subject | Re: [PATCH 2/3] KVM: nVMX: restore L1's EFER prior to setting the nested state | From | Paolo Bonzini <> |
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On 11/10/21 11:00, Maxim Levitsky wrote: > + /* > + * The vcpu might currently contain L2's IA32_EFER, due to the way > + * some userspace kvm users (e.g qemu) restore nested state. > + * > + * To fix this, restore its IA32_EFER to the value it would have > + * after VM exit from the nested guest. > + * > + */ > + > + vcpu->arch.efer = nested_vmx_get_vmcs12_host_efer(vcpu, vmcs12); > +
In principle the value of LOAD_HOST_EFER on exit need not be the same as on entry. But you don't need all of EFER, only EFER.LME/EFER.LMA, and those two bits must match ("the values of the LMA and LME bits in the field must each be that of the “host address-space size” VM-exit control" from the "Checks on Host Control Registers, MSRs, and SSP"; plus the "Checks Related to Address-Space Size").
At least it's worth adjusting the comment to explain that. But the root cause of the issue is just nested_vmx_check_* accessing vcpu->arch. So you can instead:
- split out of nested_vmx_check_host_state a new function nested_vmx_check_address_state_size that does
#ifdef CONFIG_X86_64 if (CC(!!(vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE) != !!(vcpu->arch.efer & EFER_LMA))) return -EINVAL; #endif return 0;
- call it from vmentry but not from migration
- in nested_vmx_check_host_state, assign ia32e from vmcs12->vm_exit_controls instead of vcpu->arch.efer
Paolo
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