linux-kernel - Re: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended

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Date:	Thu, 02 Jul 2015 16:49:18 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Pavel Fedin <p.fedin@...sung.com>, eric.auger@...com,
	linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
	christoffer.dall@...aro.org, andre.przywara@....com,
	kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, patches@...aro.org,
	pbonzini@...hat.com
Subject: Re: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended_msi

Hi Pavel,
On 07/02/2015 09:26 AM, Pavel Fedin wrote:
>  Hello!
> 
>> -----Original Message-----
>> From: kvm-owner@...r.kernel.org [mailto:kvm-owner@...r.kernel.org] On Behalf Of Eric Auger
>> Sent: Monday, June 29, 2015 6:37 PM
>> To: eric.auger@...com; eric.auger@...aro.org; linux-arm-kernel@...ts.infradead.org;
>> marc.zyngier@....com; christoffer.dall@...aro.org; andre.przywara@....com;
>> kvmarm@...ts.cs.columbia.edu; kvm@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org; patches@...aro.org; p.fedin@...sung.com; pbonzini@...hat.com
>> Subject: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended_msi
>>
>> On ARM, the MSI msg (address and data) comes along with
>> out-of-band device ID information. The device ID encodes the device
>> that composes the MSI msg. Let's create a new routing entry type,
>> dubbed KVM_IRQ_ROUTING_EXTENDED_MSI and use the __u32 pad space
>> to convey the device ID.
>>
>> Signed-off-by: Eric Auger <eric.auger@...aro.org>
>>
>> ---
>>
>> RFC -> PATCH
>> - remove kvm_irq_routing_extended_msi and use union instead
>> ---
>>  Documentation/virtual/kvm/api.txt | 9 ++++++++-
>>  include/uapi/linux/kvm.h          | 6 +++++-
>>  2 files changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>> index d20fd94..6426ae9 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -1414,7 +1414,10 @@ struct kvm_irq_routing_entry {
>>  	__u32 gsi;
>>  	__u32 type;
>>  	__u32 flags;
>> -	__u32 pad;
>> +	union {
>> +		__u32 pad;
>> +		__u32 devid;
>> +	};
>>  	union {
>>  		struct kvm_irq_routing_irqchip irqchip;
>>  		struct kvm_irq_routing_msi msi;
> 
>  devid is actually a part of MSI bunch. Shouldn't it be a part of struct kvm_irq_routing_msi then?
> It also has reserved pad.
Well this makes sense to me to associate the devid to the msi and put
devid in the pad field of struct kvm_irq_routing_msi.

André, Christoffer, would you agree on this change? - I would like to
avoid doing/undoing things ;-) -

> 
>> @@ -1427,6 +1430,10 @@ struct kvm_irq_routing_entry {
>>  #define KVM_IRQ_ROUTING_IRQCHIP 1
>>  #define KVM_IRQ_ROUTING_MSI 2
>>  #define KVM_IRQ_ROUTING_S390_ADAPTER 3
>> +#define KVM_IRQ_ROUTING_EXTENDED_MSI 4
>> +
>> +In case of KVM_IRQ_ROUTING_EXTENDED_MSI routing type, devid is used to convey
>> +the device ID.
>>
>>  No flags are specified so far, the corresponding field must be set to zero.
> 
> What if we use KVM_MSI_VALID_DEVID flag instead of new KVM_IRQ_ROUTING_EXTENDED_MSI definition? I
> believe this would make an API more consistent and introduce less new definitions.
do you mean using type == KVM_IRQ_ROUTING_MSI and flag ==
KVM_MSI_VALID_DEVID? Not sure this is simpler/clearer. s390 paved the
way for new routing entry types. I add a new one here.

Another solution may be to use new KVM_IRQ_ROUTING_EXTENDED_MSI type and
add struct kvm_msi ext_msi in kvm_irq_routing_entry union. It is 8 words
as well. But most probably this is even uglier.

Let's see if this thread is heading to a consensus...

Best Regards

Eric
> 
>>
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 2a23705..8484681 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -841,12 +841,16 @@ struct kvm_irq_routing_s390_adapter {
>>  #define KVM_IRQ_ROUTING_IRQCHIP 1
>>  #define KVM_IRQ_ROUTING_MSI 2
>>  #define KVM_IRQ_ROUTING_S390_ADAPTER 3
>> +#define KVM_IRQ_ROUTING_EXTENDED_MSI 4
>>
>>  struct kvm_irq_routing_entry {
>>  	__u32 gsi;
>>  	__u32 type;
>>  	__u32 flags;
>> -	__u32 pad;
>> +	union {
>> +		__u32 pad;
>> +		__u32 devid;
>> +	};
>>  	union {
>>  		struct kvm_irq_routing_irqchip irqchip;
>>  		struct kvm_irq_routing_msi msi;
>> --
>> 1.9.1
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe kvm" in
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> 
> Kind regards,
> Pavel Fedin
> Expert Engineer
> Samsung Electronics Research center Russia
> 

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