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

[Paolo Bonzini]

On 22/06/21 19:22, 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@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   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;
>   		return false;
>   	case EXIT_REASON_EXTERNAL_INTERRUPT:
>   		return true;
> diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h
> index de3b04d4b587..4b9957e2bf5b 100644
> --- a/arch/x86/kvm/vmx/vmcs.h
> +++ b/arch/x86/kvm/vmx/vmcs.h
> @@ -117,6 +117,11 @@ static inline bool is_gp_fault(u32 intr_info)
>   	return is_exception_n(intr_info, GP_VECTOR);
>   }
>   
> +static inline bool is_alignment_check(u32 intr_info)
> +{
> +	return is_exception_n(intr_info, AC_VECTOR);
> +}
> +
>   static inline bool is_machine_check(u32 intr_info)
>   {
>   	return is_exception_n(intr_info, MC_VECTOR);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index ab6f682645d7..46d9ce39249d 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4743,7 +4743,7 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
>    *  - Guest has #AC detection enabled in CR0
>    *  - Guest EFLAGS has AC bit set
>    */
> -static inline bool guest_inject_ac(struct kvm_vcpu *vcpu)
> +bool vmx_guest_inject_ac(struct kvm_vcpu *vcpu)
>   {
>   	if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
>   		return true;
> @@ -4851,7 +4851,7 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
>   		kvm_run->debug.arch.exception = ex_no;
>   		break;
>   	case AC_VECTOR:
> -		if (guest_inject_ac(vcpu)) {
> +		if (vmx_guest_inject_ac(vcpu)) {
>   			kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
>   			return 1;
>   		}
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 5740f8e2aa23..3979a947933a 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -376,6 +376,7 @@ void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
>   void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
>   u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
>   
> +bool vmx_guest_inject_ac(struct kvm_vcpu *vcpu);
>   void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu);
>   void vmx_update_msr_bitmap(struct kvm_vcpu *vcpu);
>   bool vmx_nmi_blocked(struct kvm_vcpu *vcpu);

Queued with Cc to stable, thanks.

Paolo