[RFC,v3,3/3] ARM: KVM: Check KVM_CAP_ARM_IRQ_LINE_LAYOUT_2 for smp_cpus > 256
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Message ID 20190913095639.25447-4-eric.auger@redhat.com
State New
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Series
  • KVM/ARM: Fix >256 vcpus
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Commit Message

Eric Auger Sept. 13, 2019, 9:56 a.m. UTC
Host kernel within [4.18, 5.3] report an erroneous KVM_MAX_VCPUS=512
for ARM. The actual capability to instantiate more than 256 vcpus
was fixed in 5.4 with the upgrade of the KVM_IRQ_LINE ABI to support
vcpu id encoded on 12 bits instead of 8 and a redistributor consuming
a single KVM IO device instead of 2.

So let's check this capability when attempting to use more than 256
vcpus within any ARM kvm accelerated machine.

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---

v2 -> v3:
- Implement the check in kvm_arch_init as suggested by Peter
---
 target/arm/kvm.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Comments

Richard Henderson Sept. 14, 2019, 2:36 p.m. UTC | #1
On 9/13/19 5:56 AM, Eric Auger wrote:
> Host kernel within [4.18, 5.3] report an erroneous KVM_MAX_VCPUS=512
> for ARM. The actual capability to instantiate more than 256 vcpus
> was fixed in 5.4 with the upgrade of the KVM_IRQ_LINE ABI to support
> vcpu id encoded on 12 bits instead of 8 and a redistributor consuming
> a single KVM IO device instead of 2.
> 
> So let's check this capability when attempting to use more than 256
> vcpus within any ARM kvm accelerated machine.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~
Andrew Jones Sept. 16, 2019, 2:52 p.m. UTC | #2
On Fri, Sep 13, 2019 at 11:56:39AM +0200, Eric Auger wrote:
> Host kernel within [4.18, 5.3] report an erroneous KVM_MAX_VCPUS=512
> for ARM. The actual capability to instantiate more than 256 vcpus
> was fixed in 5.4 with the upgrade of the KVM_IRQ_LINE ABI to support
> vcpu id encoded on 12 bits instead of 8 and a redistributor consuming
> a single KVM IO device instead of 2.
> 
> So let's check this capability when attempting to use more than 256
> vcpus within any ARM kvm accelerated machine.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> ---
> 
> v2 -> v3:
> - Implement the check in kvm_arch_init as suggested by Peter
> ---
>  target/arm/kvm.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index b10581fa06..b473c63edb 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -182,6 +182,7 @@ int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
>  
>  int kvm_arch_init(MachineState *ms, KVMState *s)
>  {
> +    int ret = 0;
>      /* For ARM interrupt delivery is always asynchronous,
>       * whether we are using an in-kernel VGIC or not.
>       */
> @@ -195,7 +196,14 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>  
>      cap_has_mp_state = kvm_check_extension(s, KVM_CAP_MP_STATE);
>  
> -    return 0;
> +    if (ms->smp.cpus > 256 &&
> +        !kvm_check_extension(s, KVM_CAP_ARM_IRQ_LINE_LAYOUT_2)) {
> +        error_report("Using more than 256 vcpus requires a host kernel "
> +                     "with KVM_CAP_ARM_IRQ_LINE_LAYOUT_2");
> +        ret = -EINVAL;
> +    }
> +
> +    return ret;
>  }
>  
>  unsigned long kvm_arch_vcpu_id(CPUState *cpu)
> -- 
> 2.20.1
> 
>

Reviewed-by: Andrew Jones <drjones@redhat.com>

Patch
diff mbox series

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index b10581fa06..b473c63edb 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -182,6 +182,7 @@  int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
 
 int kvm_arch_init(MachineState *ms, KVMState *s)
 {
+    int ret = 0;
     /* For ARM interrupt delivery is always asynchronous,
      * whether we are using an in-kernel VGIC or not.
      */
@@ -195,7 +196,14 @@  int kvm_arch_init(MachineState *ms, KVMState *s)
 
     cap_has_mp_state = kvm_check_extension(s, KVM_CAP_MP_STATE);
 
-    return 0;
+    if (ms->smp.cpus > 256 &&
+        !kvm_check_extension(s, KVM_CAP_ARM_IRQ_LINE_LAYOUT_2)) {
+        error_report("Using more than 256 vcpus requires a host kernel "
+                     "with KVM_CAP_ARM_IRQ_LINE_LAYOUT_2");
+        ret = -EINVAL;
+    }
+
+    return ret;
 }
 
 unsigned long kvm_arch_vcpu_id(CPUState *cpu)