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

[Peter Maydell]

On Thu, 10 Aug 2023 at 12:29, Andrew Jones <ajones@ventanamicro.com> wrote:
>
>
> Hi Paolo,
>
> Is this good for 8.1?

Is it fixing a regression since 8.0 ?

thanks
-- PMM

>
> Thanks,
> drew
>
>
> On Tue, Jul 25, 2023 at 02:26:02PM +0200, 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>
> > ---
> >
> > 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;
> >  }
> >
> > --
> > 2.41.0
> >