Re: [Qemu-devel] [PATCH 5/5] intel_iommu: do not allow EIM without KVM support

[Paolo Bonzini]

On 22/09/2016 23:04, Radim Krčmář wrote:
> Cluster x2APIC cannot work without KVM's x2apic API when the maximal
> APIC ID is > 8.  Make the code simpler by completely forbidding EIM
> without KVM's x2apic API.
> 
> Signed-off-by: Radim Krčmář <address@hidden>
> ---
>   I think it the dependency would be nicer in the eim setter, but the
>   other dependency, for interrupt remapping, isn't there and I didn't
>   venture for reasons.
> ---
>  hw/i386/intel_iommu.c  |  7 +++++++
>  target-i386/kvm-stub.c |  5 +++++
>  target-i386/kvm.c      | 13 +++++++++++++
>  target-i386/kvm_i386.h |  1 +
>  4 files changed, 26 insertions(+)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 269e37e71af4..0304a1bf6f1d 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -32,6 +32,7 @@
>  #include "hw/pci-host/q35.h"
>  #include "sysemu/kvm.h"
>  #include "hw/i386/apic_internal.h"
> +#include "kvm_i386.h"
>  
>  /*#define DEBUG_INTEL_IOMMU*/
>  #ifdef DEBUG_INTEL_IOMMU
> @@ -2485,6 +2486,12 @@ static void vtd_realize(DeviceState *dev, Error **errp)
>                       "kernel-irqchip=on, please use 'split|off'.");
>          exit(1);
>      }
> +
> +    if (s->eim_supported && kvm_irqchip_in_kernel() &&
> +        !kvm_enable_x2apic()) {
> +        error_report("EIM requires support from the KVM side (X2APIC_API).");
> +        exit(1);
> +    }
>  }
>  
>  static void vtd_class_init(ObjectClass *klass, void *data)
> diff --git a/target-i386/kvm-stub.c b/target-i386/kvm-stub.c
> index cdf15061091d..bda4dc2f0c57 100644
> --- a/target-i386/kvm-stub.c
> +++ b/target-i386/kvm-stub.c
> @@ -25,6 +25,11 @@ bool kvm_has_smm(void)
>      return 1;
>  }
>  
> +bool kvm_enable_x2apic(void)
> +{
> +    return false;
> +}
> +
>  /* This function is only called inside conditionals which we
>   * rely on the compiler to optimize out when CONFIG_KVM is not
>   * defined.
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index f1ad805665ad..4c0a4df5eaea 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -128,6 +128,19 @@ bool kvm_allows_irq0_override(void)
>      return !kvm_irqchip_in_kernel() || kvm_has_gsi_routing();
>  }
>  
> +static bool kvm_x2apic_api_set_flags(uint64_t flags)
> +{
> +    KVMState *s = KVM_STATE(current_machine->accelerator);
> +
> +    return !kvm_vm_enable_cap(s, KVM_CAP_X2APIC_API, 0, flags);
> +}
> +
> +bool kvm_enable_x2apic(void)
> +{
> +    return kvm_x2apic_api_set_flags(KVM_X2APIC_API_USE_32BIT_IDS |
> +                                    KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK);
> +}
> +
>  static int kvm_get_tsc(CPUState *cs)
>  {
>      X86CPU *cpu = X86_CPU(cs);
> diff --git a/target-i386/kvm_i386.h b/target-i386/kvm_i386.h
> index 42b00af1b1c3..559dd8b5acd2 100644
> --- a/target-i386/kvm_i386.h
> +++ b/target-i386/kvm_i386.h
> @@ -41,4 +41,5 @@ int kvm_device_msix_set_vector(KVMState *s, uint32_t 
> dev_id, uint32_t vector,
>  int kvm_device_msix_assign(KVMState *s, uint32_t dev_id);
>  int kvm_device_msix_deassign(KVMState *s, uint32_t dev_id);
>  
> +bool kvm_enable_x2apic(void);
>  #endif
> 

Since the whole IOMMU feature is new and somewhat experimental, I think
it's okay to just make EIM the default for >=2.8 machine types if KVM is
on (using DEFINE_PROP_ON_OFF_AUTO; auto means true if KVM is on and
false otherwise, and pc-2.7 would set eim=off). It means requiring
kernel 4.8 by default, but I don't think it's a big deal.

Paolo