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

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 6/23/2021 1:22 AM, Sean Christopherson wrote:
> Mark #ACs that won't be reinjected to the guest as wanted by L0 so that
> KVM handles split-lock #AC from L2 instead of forwarding the exception to
> L1.  Split-lock #AC isn't yet virtualized, i.e. L1 will treat it like a
> regular #AC and do the wrong thing, e.g. reinject it into L2.
> 
> Fixes: e6f8b6c12f03 ("KVM: VMX: Extend VMXs #AC interceptor to handle split lock #AC in guest")
> Cc: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/kvm/vmx/nested.c | 3 +++
>   arch/x86/kvm/vmx/vmcs.h   | 5 +++++
>   arch/x86/kvm/vmx/vmx.c    | 4 ++--
>   arch/x86/kvm/vmx/vmx.h    | 1 +
>   4 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 183fd9d62fc5..fa3f50f0a3fa 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5833,6 +5833,9 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
>   		else if (is_breakpoint(intr_info) &&
>   			 vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
>   			return true;
> +		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()?

>   		return false;
>   	case EXIT_REASON_EXTERNAL_INTERRUPT:
>   		return true;