Re: [PATCH v2 09/11] KVM: SVM: Add VNMI bit definition

[Santosh Shukla]

On 2/1/2023 4:12 AM, Sean Christopherson wrote:
> On Tue, Nov 29, 2022, Maxim Levitsky wrote:
>> From: Santosh Shukla <santosh.shukla@xxxxxxx>
>>
>> VNMI exposes 3 capability bits (V_NMI, V_NMI_MASK, and V_NMI_ENABLE) to
>> virtualize NMI and NMI_MASK, Those capability bits are part of
>> VMCB::intr_ctrl -
>> V_NMI(11) - Indicates whether a virtual NMI is pending in the guest.
>> V_NMI_MASK(12) - Indicates whether virtual NMI is masked in the guest.
>> V_NMI_ENABLE(26) - Enables the NMI virtualization feature for the guest.
>>
>> When Hypervisor wants to inject NMI, it will set V_NMI bit, Processor
>> will clear the V_NMI bit and Set the V_NMI_MASK which means the Guest is
>> handling NMI, After the guest handled the NMI, The processor will clear
>> the V_NMI_MASK on the successful completion of IRET instruction Or if
>> VMEXIT occurs while delivering the virtual NMI.
>>
>> To enable the VNMI capability, Hypervisor need to program
>> V_NMI_ENABLE bit 1.
>>
>> Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
>> Signed-off-by: Santosh Shukla <santosh.shukla@xxxxxxx>
>> ---
>>  arch/x86/include/asm/svm.h | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
>> index cb1ee53ad3b189..26d6f549ce2b46 100644
>> --- a/arch/x86/include/asm/svm.h
>> +++ b/arch/x86/include/asm/svm.h
>> @@ -203,6 +203,13 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
>>  #define X2APIC_MODE_SHIFT 30
>>  #define X2APIC_MODE_MASK (1 << X2APIC_MODE_SHIFT)
>>  
>> +#define V_NMI_PENDING_SHIFT 11
>> +#define V_NMI_PENDING (1 << V_NMI_PENDING_SHIFT)
>> +#define V_NMI_MASK_SHIFT 12
>> +#define V_NMI_MASK (1 << V_NMI_MASK_SHIFT)
> 
> Argh, more KVM warts.  The existing INT_CTL defines all use "mask" in the name,
> so looking at V_NMI_MASK in the context of other code reads "vNMI is pending",
> not "vNMIs are blocked".
> 
> IMO, the existing _MASK terminology is the one that's wrong, but there's an absurd
> amount of prior art in svm.h :-(
> 
> And the really annoying one is V_INTR_MASKING_MASK, which IIRC says "virtual INTR
> masking is enabled", not "virtual INTRs are blocked".
> 
> So maybe call this V_NMI_BLOCKING_MASK?  And tack on _MASK too the others (even
> though I agree it's ugly).
> 

Sure.

>> +#define V_NMI_ENABLE_SHIFT 26
>> +#define V_NMI_ENABLE (1 << V_NMI_ENABLE_SHIFT)
> 
> Hrm.  I think I would prefer to keep the defines ordered by bit position.  Knowing
> that there's an enable bit isn't all that critical for understanding vNMI pending
> and blocked.

Sure, Sean will include in V3.

Thanks,
Santosh