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

[Andrew Jones]

On Thu, Aug 10, 2023 at 12:38:28PM +0100, Peter Maydell wrote:
> 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 ?

The fix is for running with KVM which includes 00f918f61c56, which is
v6.5-rc1 and later. All QEMU versions will fail to start, so this fix
isn't fixing a QEMU regression, but until this fix, or the KVM AIA
support series, is merged, then we won't have any QEMU version we can
use with later KVM.

Thanks,
drew

> 
> 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
> > >