Re: [PATCH] KVM: nVMX: Handle split-lock #AC exceptions that happen in L2

[Paolo Bonzini]

On 23/06/21 04:43, Xiaoyao Li wrote:
> > +        else if (is_alignment_check(intr_info) &&
> > +             !vmx_guest_inject_ac(vcpu))
> > +            return true;
>
> Why choose to check in nested_vmx_l0_wants_exit, not in 
> nested_vmx_l1_wants_exit()?

nested_vmx_l0_wants_exit() == true means "this is a vmexit that needs 
some transformation before being injected into L1".  Instead, 
nested_vmx_l1_wants_exit() == true means "this is an event that should 
either be processed directly by L0, or cause a vmexit in L1"

Typically, nested_vmx_l1_wants_exit() checks the controls in vmcs12, 
while nested_vmx_l0_wants_exit() returns true unconditionally for most 
vmexits; for others it checks processor state, or other state set up by 
userspace with ioctls such as vcpu->guest_debug.

In this case it's *L0* that wants that vmexit, in order to either 
disable split-lock detection or inject a SIGBUS, so 
nested_vmx_l0_wants_exit() is the right one to test.

Paolo