Re: [PATCH v2 05/15] KVM: x86: Trace hypercall register *after* truncating values for 32-bit

[Binbin Wu]

On 5/15/2026 5:53 AM, Sean Christopherson wrote:
> When tracing hypercalls, invoke the tracepoint *after* truncating the
> register values for 32-bit guests so as not to record unused garbage (in
> the extremely unlikely scenario that the guest left garbage in a register
> after transitioning from 64-bit mode to 32-bit mode).
> 
> Fixes: 229456fc34b1 ("KVM: convert custom marker based tracing to event traces")
> Reviewed-by: Yosry Ahmed <yosry@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

> ---
>  arch/x86/kvm/x86.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 209eae67ab18..23b3957b9ae0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10430,8 +10430,6 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, int cpl,
>  
>  	++vcpu->stat.hypercalls;
>  
> -	trace_kvm_hypercall(nr, a0, a1, a2, a3);
> -
>  	if (!op_64_bit) {
>  		nr &= 0xFFFFFFFF;
>  		a0 &= 0xFFFFFFFF;
> @@ -10440,6 +10438,8 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, int cpl,
>  		a3 &= 0xFFFFFFFF;
>  	}
>  
> +	trace_kvm_hypercall(nr, a0, a1, a2, a3);
> +
>  	if (cpl) {
>  		ret = -KVM_EPERM;
>  		goto out;