Re: [PATCH v2] kvm: Remove KVM_CREATE_IRQCHIP support assumption

[Daniel Henrique Barboza]

On 7/25/23 09:26, Andrew Jones wrote:
> Since Linux commit 00f918f61c56 ("RISC-V: KVM: Skeletal in-kernel AIA
> irqchip support") checking KVM_CAP_IRQCHIP returns non-zero when the
> RISC-V platform has AIA. The cap indicates KVM supports at least one
> of the following ioctls:
>
>    KVM_CREATE_IRQCHIP
>    KVM_IRQ_LINE
>    KVM_GET_IRQCHIP
>    KVM_SET_IRQCHIP
>    KVM_GET_LAPIC
>    KVM_SET_LAPIC
>
> but the cap doesn't imply that KVM must support any of those ioctls
> in particular. However, QEMU was assuming the KVM_CREATE_IRQCHIP
> ioctl was supported. Stop making that assumption by introducing a
> KVM parameter that each architecture which supports KVM_CREATE_IRQCHIP
> sets. Adding parameters isn't awesome, but given how the
> KVM_CAP_IRQCHIP isn't very helpful on its own, we don't have a lot of
> options.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> ---

Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

> While this fixes booting guests on riscv KVM with AIA it's unlikely
> to get merged before the QEMU support for KVM AIA[1] lands, which
> would also fix the issue. I think this patch is still worth considering
> though since QEMU's assumption is wrong.
>
> [1] https://lore.kernel.org/all/20230714084429.22349-1-yongxuan.wang@sifive.com/
>
> v2:
>    - Move the s390x code to an s390x file. [Thomas]
>    - Drop the KVM_CAP_IRQCHIP check from the top of kvm_irqchip_create(),
>      as it's no longer necessary.
>
>   accel/kvm/kvm-all.c    | 16 ++++------------
>   include/sysemu/kvm.h   |  1 +
>   target/arm/kvm.c       |  3 +++
>   target/i386/kvm/kvm.c  |  2 ++
>   target/s390x/kvm/kvm.c | 11 +++++++++++
>   5 files changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 373d876c0580..cddcb6eca641 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -86,6 +86,7 @@ struct KVMParkedVcpu {
>   };
>   
>   KVMState *kvm_state;
> +bool kvm_has_create_irqchip;
>   bool kvm_kernel_irqchip;
>   bool kvm_split_irqchip;
>   bool kvm_async_interrupts_allowed;
> @@ -2358,17 +2359,6 @@ static void kvm_irqchip_create(KVMState *s)
>       int ret;
>   
>       assert(s->kernel_irqchip_split != ON_OFF_AUTO_AUTO);
> -    if (kvm_check_extension(s, KVM_CAP_IRQCHIP)) {
> -        ;
> -    } else if (kvm_check_extension(s, KVM_CAP_S390_IRQCHIP)) {
> -        ret = kvm_vm_enable_cap(s, KVM_CAP_S390_IRQCHIP, 0);
> -        if (ret < 0) {
> -            fprintf(stderr, "Enable kernel irqchip failed: %s\n", 
> strerror(-ret));
> -            exit(1);
> -        }
> -    } else {
> -        return;
> -    }
>   
>       /* First probe and see if there's a arch-specific hook to create the
>        * in-kernel irqchip for us */
> @@ -2377,8 +2367,10 @@ static void kvm_irqchip_create(KVMState *s)
>           if (s->kernel_irqchip_split == ON_OFF_AUTO_ON) {
>               error_report("Split IRQ chip mode not supported.");
>               exit(1);
> -        } else {
> +        } else if (kvm_has_create_irqchip) {
>               ret = kvm_vm_ioctl(s, KVM_CREATE_IRQCHIP);
> +        } else {
> +            return;
>           }
>       }
>       if (ret < 0) {
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index 115f0cca79d1..84b1bb3dc91e 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -32,6 +32,7 @@
>   #ifdef CONFIG_KVM_IS_POSSIBLE
>   
>   extern bool kvm_allowed;
> +extern bool kvm_has_create_irqchip;
>   extern bool kvm_kernel_irqchip;
>   extern bool kvm_split_irqchip;
>   extern bool kvm_async_interrupts_allowed;
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index b4c7654f4980..2fa87b495d68 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -250,6 +250,9 @@ int kvm_arm_get_max_vm_ipa_size(MachineState *ms, bool 
> *fixed_ipa)
>   int kvm_arch_init(MachineState *ms, KVMState *s)
>   {
>       int ret = 0;
> +
> +    kvm_has_create_irqchip = kvm_check_extension(s, KVM_CAP_IRQCHIP);
> +
>       /* For ARM interrupt delivery is always asynchronous,
>        * whether we are using an in-kernel VGIC or not.
>        */
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index ebfaf3d24c79..6363e67f092d 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -2771,6 +2771,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>           }
>       }
>   
> +    kvm_has_create_irqchip = kvm_check_extension(s, KVM_CAP_IRQCHIP);
> +
>       return 0;
>   }
>   
> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
> index a9e5880349d9..bcc735227f7d 100644
> --- a/target/s390x/kvm/kvm.c
> +++ b/target/s390x/kvm/kvm.c
> @@ -391,6 +391,17 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>       }
>   
>       kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
> +
> +    kvm_has_create_irqchip = kvm_check_extension(s, KVM_CAP_S390_IRQCHIP);
> +    if (kvm_has_create_irqchip) {
> +        int ret = kvm_vm_enable_cap(s, KVM_CAP_S390_IRQCHIP, 0);
> +
> +        if (ret < 0) {
> +            fprintf(stderr, "Enable kernel irqchip failed: %s\n", 
> strerror(-ret));
> +            exit(1);
> +        }
> +    }
> +
>       return 0;
>   }
>