Re: [PATCH v5 2/2] x86/svm: Use the virtual NMI when available

[Teddy Astie <teddy.astie@xxxxxxxxxx>]

Le 26/02/2026 à 14:23, Abdelkareem Abdelsaamad a écrit :
> With the Virtual NMI (vNMI), the pending NMI is simply stuffed into the VMCB
> and handed off to the hardware. There is no need for the artificial tracking
> of the NMI handling completion with the IRET instruction interception.
> 
> Adjust the svm_inject_nmi to rather inject the NMIs using the vNMI Hardware
> accelerated feature when the AMD platform supports the vNMI.
> 
> Signed-off-by: Abdelkareem Abdelsaamad <abdelkareem.abdelsaamad@xxxxxxxxxx>
> ---
>   xen/arch/x86/hvm/svm/intr.c | 6 ++++++
>   xen/arch/x86/hvm/svm/svm.c  | 1 +
>   xen/arch/x86/hvm/svm/vmcb.c | 2 ++
>   3 files changed, 9 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/svm/intr.c b/xen/arch/x86/hvm/svm/intr.c
> index 6453a46b85..112a393211 100644
> --- a/xen/arch/x86/hvm/svm/intr.c
> +++ b/xen/arch/x86/hvm/svm/intr.c
> @@ -33,6 +33,12 @@ static void svm_inject_nmi(struct vcpu *v)
>       u32 general1_intercepts = vmcb_get_general1_intercepts(vmcb);
>       intinfo_t event;
>   
> +    if ( vmcb->_vintr.fields.vnmi_enable )
> +    {
> +        vmcb->_vintr.fields.vnmi_pending = 1;
> +        return;
> +    }
> +
>       event.raw = 0;
>       event.v = true;
>       event.type = X86_ET_NMI;
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> index 18ba837738..815565c33f 100644
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -2524,6 +2524,7 @@ const struct hvm_function_table * __init start_svm(void)
>       P(cpu_has_tsc_ratio, "TSC Rate MSR");
>       P(cpu_has_svm_sss, "NPT Supervisor Shadow Stack");
>       P(cpu_has_svm_spec_ctrl, "MSR_SPEC_CTRL virtualisation");
> +    P(cpu_has_svm_vnmi, "Virtual NMI");
>       P(cpu_has_svm_bus_lock, "Bus Lock Filter");
>   #undef P
>   
> diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
> index e583ef8548..e90bbac332 100644
> --- a/xen/arch/x86/hvm/svm/vmcb.c
> +++ b/xen/arch/x86/hvm/svm/vmcb.c
> @@ -184,6 +184,8 @@ static int construct_vmcb(struct vcpu *v)
>       if ( default_xen_spec_ctrl == SPEC_CTRL_STIBP )
>           v->arch.msrs->spec_ctrl.raw = SPEC_CTRL_STIBP;
>   
> +    vmcb->_vintr.fields.vnmi_enable = cpu_has_svm_vnmi;
> +
>       return 0;
>   }
>   

What is the status of this ?

IIRC the main concern was regarding whether or not the vnmi_pending bit 
requires to set the clean_bits. But it seems it is not the case here.

Do we have a official confirmation on that ?

Teddy


--
Teddy Astie | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech