[PATCH kernel v3] KVM: PPC: Make KVM_CAP_IRQFD_RESAMPLE support platform dependent

[Marc Zyngier]

On Wed, 21 Sep 2022 05:49:25 +0100,
Alexey Kardashevskiy <aik at ozlabs.ru> wrote:
> 
> When introduced, IRQFD resampling worked on POWER8 with XICS. However
> KVM on POWER9 has never implemented it - the compatibility mode code
> ("XICS-on-XIVE") misses the kvm_notify_acked_irq() call and the native
> XIVE mode does not handle INTx in KVM at all.
> 
> This moved the capability support advertising to platforms and stops
> advertising it on XIVE, i.e. POWER9 and later.
> 
> This stops advertising the capability on MIPS and RISC-V as these
> do not select HAVE_KVM_IRQFD and do not implement IRQFD resampling
> anyway.

This paragraph makes no sense. Not selecting HAVE_KVM_IRQFD, by
definition, prevents the advertising of the capability. Hell, you are
even removing it from a block guarded by "#ifdef CONFIG_HAVE_KVM_IRQFD".

> 
> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
> Acked-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> Changes:
> v3:
> * removed all ifdeferry
> * removed the capability for MIPS and RISCV
> * adjusted the commit log about MIPS and RISCV
> 
> v2:
> * removed ifdef for ARM64.
> ---
>  arch/arm64/kvm/arm.c       | 1 +
>  arch/powerpc/kvm/powerpc.c | 6 ++++++
>  arch/s390/kvm/kvm-s390.c   | 1 +
>  arch/x86/kvm/x86.c         | 1 +
>  virt/kvm/kvm_main.c        | 1 -
>  5 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 2ff0ef62abad..d2daa4d375b5 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -218,6 +218,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_VCPU_ATTRIBUTES:
>  	case KVM_CAP_PTP_KVM:
>  	case KVM_CAP_ARM_SYSTEM_SUSPEND:
> +	case KVM_CAP_IRQFD_RESAMPLE:
>  		r = 1;
>  		break;
>  	case KVM_CAP_SET_GUEST_DEBUG2:
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index fb1490761c87..908ce8bd91c9 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -593,6 +593,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		break;
>  #endif
>  
> +#ifdef CONFIG_HAVE_KVM_IRQFD
> +	case KVM_CAP_IRQFD_RESAMPLE:
> +		r = !xive_enabled();
> +		break;
> +#endif
> +
>  	case KVM_CAP_PPC_ALLOC_HTAB:
>  		r = hv_enabled;
>  		break;
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index edfd4bbd0cba..7521adadb81b 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -577,6 +577,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_SET_GUEST_DEBUG:
>  	case KVM_CAP_S390_DIAG318:
>  	case KVM_CAP_S390_MEM_OP_EXTENSION:
> +	case KVM_CAP_IRQFD_RESAMPLE:
>  		r = 1;
>  		break;
>  	case KVM_CAP_SET_GUEST_DEBUG2:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 43a6a7efc6ec..2d6c5a8fdf14 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4395,6 +4395,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_VAPIC:
>  	case KVM_CAP_ENABLE_CAP:
>  	case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES:
> +	case KVM_CAP_IRQFD_RESAMPLE:
>  		r = 1;
>  		break;
>  	case KVM_CAP_EXIT_HYPERCALL:
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 584a5bab3af3..05cf94013f02 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4447,7 +4447,6 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  #endif
>  #ifdef CONFIG_HAVE_KVM_IRQFD
>  	case KVM_CAP_IRQFD:
> -	case KVM_CAP_IRQFD_RESAMPLE:
>  #endif

Do you see what I mean?

>  	case KVM_CAP_IOEVENTFD_ANY_LENGTH:
>  	case KVM_CAP_CHECK_EXTENSION_VM:

So, with the nonsensical paragraph removed from the commit log:

Acked-by: Marc Zyngier <maz at kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.