2017-06-28 14:56+0200, Paolo Bonzini: > On 28/06/2017 14:25, Wanpeng Li wrote: >> From: Wanpeng Li <[email protected]> >> >> Add an nested_apf field to vcpu->arch.exception to identify an async page >> fault, and constructs the expected vm-exit information fields. Force a >> nested VM exit from nested_vmx_check_exception() if the injected #PF is >> async page fault. Extending the userspace interface KVM_GET_VCPU_EVENTS >> and KVM_SET_VCPU_EVENTS for live migration. >> >> Cc: Paolo Bonzini <[email protected]> >> Cc: Radim Krčmář <[email protected]> >> Signed-off-by: Wanpeng Li <[email protected]> >> --- > > Radim, Wanpeng, > > the patch is nice now but I'm still not 100% sure about the live > migration part. Why do we need to pass nested_apf to userspace, but not > nested_apf_token?
We do not need it for migration, but unavailable nested_apf_token already breaks checkpoint & restore from userspace ... I think the cleanest way would be to add a new paravirtual event for nested_apf. (Or just keep delaying the apf.) Migration does a "async-pf-broadcast" while setting the async-pf MSR on destination, which resumes all async-pf waiters. Userspace actually has to drop the async-pf event on migration, because the destination has invalid nested_apf_token. (It's a horrible design.) nested_apf is not #PF: if we didn't pass nested_apf, then the exception would be injected as #PF to L2 after migration. (Local KVM could remember that the #PF is nested_apf and do some ugly hacks.)
