Re: [PATCH v3 2/2] x86/svm: Use the virtual NMI when available

["Teddy Astie" <teddy.astie@xxxxxxxxxx>]

Le 16/02/2026 à 11:16, Andrew Cooper a écrit :
> On 16/02/2026 10:07 am, Teddy Astie wrote:
>> Le 15/02/2026 à 19:24, 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 support the vNMI.
>>>
>>> Adjust the svm_get_interrupt_shadow to check if the vNMI is currently 
>>> blocked
>>> by servicing another in-progress NMI.
>>>
>>> Signed-off-by: Abdelkareem Abdelsaamad <abdelkareem.abdelsaamad@xxxxxxxxxx>
>>> ---
>>>    xen/arch/x86/hvm/svm/intr.c | 9 +++++++++
>>>    xen/arch/x86/hvm/svm/svm.c  | 5 ++++-
>>>    xen/arch/x86/hvm/svm/vmcb.c | 2 ++
>>>    3 files changed, 15 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/xen/arch/x86/hvm/svm/intr.c b/xen/arch/x86/hvm/svm/intr.c
>>> index 6453a46b85..3e8959f155 100644
>>> --- a/xen/arch/x86/hvm/svm/intr.c
>>> +++ b/xen/arch/x86/hvm/svm/intr.c
>>> @@ -33,6 +33,15 @@ 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 )
>>> +    {
>>> +       if ( !vmcb->_vintr.fields.vnmi_pending &&
>>> +            !vmcb->_vintr.fields.vnmi_blocking )
>>> +           vmcb->_vintr.fields.vnmi_pending = 1;
>>> +
>>> +        return;
>>> +    }
>>> +
>> I think you need to update the clearbit for tpr (related to vintr) for
>> the hardware to know that you modified the vnmi_pending bit.
>
> What makes you think this?  The APM states otherwise.
>

The APM state doesn't appears to state regarding this; it's neither a
part of the "VMCB Clear Field" layout part nor the the "explicitely not
cached" list.

So I assume that it may be covered by the TPR clean-bit (which is the
same part of vmcb); as it's actually unclear if hardware wants it or not.

> ~Andrew
>

Teddy


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Teddy Astie | Vates XCP-ng Developer

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