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[PATCH v2] LoongArch: KVM: Advertise already-supported capabilities

Tao Cui posted 1 patch 1 month, 3 weeks ago 
arch/loongarch/kvm/vm.c | 4 ++++
1 file changed, 4 insertions(+)
[PATCH v2] LoongArch: KVM: Advertise already-supported capabilities
Posted by Tao Cui 1 month, 3 weeks ago 
Several LoongArch KVM features are fully implemented but were never
reported through their standard KVM_CHECK_EXTENSION probes, so userspace
cannot discover them.  Advertise the ones that already work and have a
real consumer:

  - KVM_CAP_STEAL_TIME: steal time works end-to-end (host-side record
    plus guest paravirt side), and the probe returns kvm_pvtime_supported().

  - KVM_CAP_VCPU_ATTRIBUTES: per-vCPU device-attribute ioctls are
    implemented (CPUCFG, PVTIME control); advertise the discovery cap.

This adds no new functionality; it only makes existing features
discoverable via the standard probe.

Signed-off-by: Tao Cui <cui.tao@linux.dev>
---
Changes in v2:
  - Drop KVM_CAP_IRQFD_RESAMPLE: the only consumer is VFIO INTx, which
    needs IOMMU/VFIO not yet available on LoongArch.
  - Drop KVM_CAP_VM_GPA_BITS: the cap implies a GPA-width setter that
    LoongArch does not implement.

 arch/loongarch/kvm/vm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
index 1317c718f896..0a51931d6f6e 100644
--- a/arch/loongarch/kvm/vm.c
+++ b/arch/loongarch/kvm/vm.c
@@ -122,6 +122,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IOEVENTFD:
 	case KVM_CAP_MP_STATE:
 	case KVM_CAP_SET_GUEST_DEBUG:
+	case KVM_CAP_VCPU_ATTRIBUTES:
 		r = 1;
 		break;
 	case KVM_CAP_NR_VCPUS:
@@ -136,6 +137,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_NR_MEMSLOTS:
 		r = KVM_USER_MEM_SLOTS;
 		break;
+	case KVM_CAP_STEAL_TIME:
+		r = kvm_pvtime_supported();
+		break;
 	default:
 		r = 0;
 		break;
Re: [PATCH v2] LoongArch: KVM: Advertise already-supported capabilities
Posted by Huacai Chen 1 month, 3 weeks ago 
Applied, thanks.

Huacai

On Wed, Aug 5, 2026 at 1:46 PM Tao Cui <cui.tao@linux.dev> wrote:
>
> Several LoongArch KVM features are fully implemented but were never
> reported through their standard KVM_CHECK_EXTENSION probes, so userspace
> cannot discover them.  Advertise the ones that already work and have a
> real consumer:
>
>   - KVM_CAP_STEAL_TIME: steal time works end-to-end (host-side record
>     plus guest paravirt side), and the probe returns kvm_pvtime_supported().
>
>   - KVM_CAP_VCPU_ATTRIBUTES: per-vCPU device-attribute ioctls are
>     implemented (CPUCFG, PVTIME control); advertise the discovery cap.
>
> This adds no new functionality; it only makes existing features
> discoverable via the standard probe.
>
> Signed-off-by: Tao Cui <cui.tao@linux.dev>
> ---
> Changes in v2:
>   - Drop KVM_CAP_IRQFD_RESAMPLE: the only consumer is VFIO INTx, which
>     needs IOMMU/VFIO not yet available on LoongArch.
>   - Drop KVM_CAP_VM_GPA_BITS: the cap implies a GPA-width setter that
>     LoongArch does not implement.
>
>  arch/loongarch/kvm/vm.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
> index 1317c718f896..0a51931d6f6e 100644
> --- a/arch/loongarch/kvm/vm.c
> +++ b/arch/loongarch/kvm/vm.c
> @@ -122,6 +122,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_IOEVENTFD:
>         case KVM_CAP_MP_STATE:
>         case KVM_CAP_SET_GUEST_DEBUG:
> +       case KVM_CAP_VCPU_ATTRIBUTES:
>                 r = 1;
>                 break;
>         case KVM_CAP_NR_VCPUS:
> @@ -136,6 +137,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_NR_MEMSLOTS:
>                 r = KVM_USER_MEM_SLOTS;
>                 break;
> +       case KVM_CAP_STEAL_TIME:
> +               r = kvm_pvtime_supported();
> +               break;
>         default:
>                 r = 0;
>                 break;
>
Re: [PATCH v2] LoongArch: KVM: Advertise already-supported capabilities
Posted by Tao Cui 1 month, 3 weeks ago 
Hi, Huacai

I missed my Signed-off-by tag for this patch, my mistake.
Could you append:
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
If it’s not workable, no problem at all.

于 2026年8月9日 GMT+08:00 12:06:36，Huacai Chen <chenhuacai@kernel.org> 写道：
>Applied, thanks.
>
>Huacai
>
>On Wed, Aug 5, 2026 at 1:46 PM Tao Cui <cui.tao@linux.dev> wrote:
>>
>> Several LoongArch KVM features are fully implemented but were never
>> reported through their standard KVM_CHECK_EXTENSION probes, so userspace
>> cannot discover them.  Advertise the ones that already work and have a
>> real consumer:
>>
>>   - KVM_CAP_STEAL_TIME: steal time works end-to-end (host-side record
>>     plus guest paravirt side), and the probe returns kvm_pvtime_supported().
>>
>>   - KVM_CAP_VCPU_ATTRIBUTES: per-vCPU device-attribute ioctls are
>>     implemented (CPUCFG, PVTIME control); advertise the discovery cap.
>>
>> This adds no new functionality; it only makes existing features
>> discoverable via the standard probe.
>>
>> Signed-off-by: Tao Cui <cui.tao@linux.dev>
>> ---
>> Changes in v2:
>>   - Drop KVM_CAP_IRQFD_RESAMPLE: the only consumer is VFIO INTx, which
>>     needs IOMMU/VFIO not yet available on LoongArch.
>>   - Drop KVM_CAP_VM_GPA_BITS: the cap implies a GPA-width setter that
>>     LoongArch does not implement.
>>
>>  arch/loongarch/kvm/vm.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
>> index 1317c718f896..0a51931d6f6e 100644
>> --- a/arch/loongarch/kvm/vm.c
>> +++ b/arch/loongarch/kvm/vm.c
>> @@ -122,6 +122,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>         case KVM_CAP_IOEVENTFD:
>>         case KVM_CAP_MP_STATE:
>>         case KVM_CAP_SET_GUEST_DEBUG:
>> +       case KVM_CAP_VCPU_ATTRIBUTES:
>>                 r = 1;
>>                 break;
>>         case KVM_CAP_NR_VCPUS:
>> @@ -136,6 +137,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>         case KVM_CAP_NR_MEMSLOTS:
>>                 r = KVM_USER_MEM_SLOTS;
>>                 break;
>> +       case KVM_CAP_STEAL_TIME:
>> +               r = kvm_pvtime_supported();
>> +               break;
>>         default:
>>                 r = 0;
>>                 break;
>>
Re: [PATCH v2] LoongArch: KVM: Advertise already-supported capabilities
Posted by Huacai Chen 1 month, 3 weeks ago 
On Mon, Aug 10, 2026 at 12:08 PM Tao Cui <cui.tao@linux.dev> wrote:
>
> Hi, Huacai
>
> I missed my Signed-off-by tag for this patch, my mistake.
> Could you append:
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
> If it’s not workable, no problem at all.
Corrected.

Huacai
>
> 于 2026年8月9日 GMT+08:00 12:06:36，Huacai Chen <chenhuacai@kernel.org> 写道：
> >Applied, thanks.
> >
> >Huacai
> >
> >On Wed, Aug 5, 2026 at 1:46 PM Tao Cui <cui.tao@linux.dev> wrote:
> >>
> >> Several LoongArch KVM features are fully implemented but were never
> >> reported through their standard KVM_CHECK_EXTENSION probes, so userspace
> >> cannot discover them.  Advertise the ones that already work and have a
> >> real consumer:
> >>
> >>   - KVM_CAP_STEAL_TIME: steal time works end-to-end (host-side record
> >>     plus guest paravirt side), and the probe returns kvm_pvtime_supported().
> >>
> >>   - KVM_CAP_VCPU_ATTRIBUTES: per-vCPU device-attribute ioctls are
> >>     implemented (CPUCFG, PVTIME control); advertise the discovery cap.
> >>
> >> This adds no new functionality; it only makes existing features
> >> discoverable via the standard probe.
> >>
> >> Signed-off-by: Tao Cui <cui.tao@linux.dev>
> >> ---
> >> Changes in v2:
> >>   - Drop KVM_CAP_IRQFD_RESAMPLE: the only consumer is VFIO INTx, which
> >>     needs IOMMU/VFIO not yet available on LoongArch.
> >>   - Drop KVM_CAP_VM_GPA_BITS: the cap implies a GPA-width setter that
> >>     LoongArch does not implement.
> >>
> >>  arch/loongarch/kvm/vm.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
> >> index 1317c718f896..0a51931d6f6e 100644
> >> --- a/arch/loongarch/kvm/vm.c
> >> +++ b/arch/loongarch/kvm/vm.c
> >> @@ -122,6 +122,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >>         case KVM_CAP_IOEVENTFD:
> >>         case KVM_CAP_MP_STATE:
> >>         case KVM_CAP_SET_GUEST_DEBUG:
> >> +       case KVM_CAP_VCPU_ATTRIBUTES:
> >>                 r = 1;
> >>                 break;
> >>         case KVM_CAP_NR_VCPUS:
> >> @@ -136,6 +137,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >>         case KVM_CAP_NR_MEMSLOTS:
> >>                 r = KVM_USER_MEM_SLOTS;
> >>                 break;
> >> +       case KVM_CAP_STEAL_TIME:
> >> +               r = kvm_pvtime_supported();
> >> +               break;
> >>         default:
> >>                 r = 0;
> >>                 break;
> >>
Re: [PATCH v2] LoongArch: KVM: Advertise already-supported capabilities
Posted by Bibo Mao 1 month, 3 weeks ago 

On 2026/8/5 下午1:45, Tao Cui wrote:
> Several LoongArch KVM features are fully implemented but were never
> reported through their standard KVM_CHECK_EXTENSION probes, so userspace
> cannot discover them.  Advertise the ones that already work and have a
> real consumer:
> 
>    - KVM_CAP_STEAL_TIME: steal time works end-to-end (host-side record
>      plus guest paravirt side), and the probe returns kvm_pvtime_supported().
> 
>    - KVM_CAP_VCPU_ATTRIBUTES: per-vCPU device-attribute ioctls are
>      implemented (CPUCFG, PVTIME control); advertise the discovery cap.
> 
> This adds no new functionality; it only makes existing features
> discoverable via the standard probe.
> 
> Signed-off-by: Tao Cui <cui.tao@linux.dev>
> ---
> Changes in v2:
>    - Drop KVM_CAP_IRQFD_RESAMPLE: the only consumer is VFIO INTx, which
>      needs IOMMU/VFIO not yet available on LoongArch.
>    - Drop KVM_CAP_VM_GPA_BITS: the cap implies a GPA-width setter that
>      LoongArch does not implement.
> 
>   arch/loongarch/kvm/vm.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
> index 1317c718f896..0a51931d6f6e 100644
> --- a/arch/loongarch/kvm/vm.c
> +++ b/arch/loongarch/kvm/vm.c
> @@ -122,6 +122,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_IOEVENTFD:
>   	case KVM_CAP_MP_STATE:
>   	case KVM_CAP_SET_GUEST_DEBUG:
> +	case KVM_CAP_VCPU_ATTRIBUTES:
>   		r = 1;
>   		break;
>   	case KVM_CAP_NR_VCPUS:
> @@ -136,6 +137,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_NR_MEMSLOTS:
>   		r = KVM_USER_MEM_SLOTS;
>   		break;
> +	case KVM_CAP_STEAL_TIME:
> +		r = kvm_pvtime_supported();
> +		break;
>   	default:
>   		r = 0;
>   		break;
> 
Reviewed-by: Bibo Mao <maobibo@loongson.cn>

Patchew 2.1-devel-ea86937

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