Re: [Qemu-devel] [PATCH v5 07/18] kvm: add kvm_arm_get_max_vm_phys_shift

[Jia He <jiakernel2@gmail.com>]

Hi Eric

On 2019/1/23 18:14, Eric Auger wrote:
> Add the kvm_arm_get_max_vm_phys_shift() helper that returns the
> log of the maximum IPA size supported by KVM. This capability
> needs to be known to create the VM with a specific IPA max size
> (kvm_type passed along KVM_CREATE_VM ioctl.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
> v3 -> v4:
> - s/s/ms in kvm_arm_get_max_vm_phys_shift function comment
> - check KVM_CAP_ARM_VM_IPA_SIZE extension
>
> v1 -> v2:
> - put this in ARM specific code
> ---
>   target/arm/kvm.c     |  8 ++++++++
>   target/arm/kvm_arm.h | 16 ++++++++++++++++
>   2 files changed, 24 insertions(+)
>
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index e00ccf9c98..877c588ef5 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -18,6 +18,7 @@
>   #include "qemu/error-report.h"
>   #include "sysemu/sysemu.h"
>   #include "sysemu/kvm.h"
> +#include "sysemu/kvm_int.h"
>   #include "kvm_arm.h"
>   #include "cpu.h"
>   #include "trace.h"
> @@ -162,6 +163,13 @@ void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
>       env->features = arm_host_cpu_features.features;
>   }
>   
> +int kvm_arm_get_max_vm_phys_shift(MachineState *ms)
> +{
> +    KVMState *s = KVM_STATE(ms->accelerator);
> +
> +    return kvm_check_extension(s, KVM_CAP_ARM_VM_IPA_SIZE);

If KVM_CAP_ARM_VM_IPA_SIZE is not supported in host kernel, would it be

better if kvm_arm_get_max_vm_phys_shift returns a default value

(e.g. 40),instead of an errno?

---
Cheers,
Jia He

> +}
> +
>   int kvm_arch_init(MachineState *ms, KVMState *s)
>   {
>       /* For ARM interrupt delivery is always asynchronous,
> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> index 6393455b1d..5969c41f83 100644
> --- a/target/arm/kvm_arm.h
> +++ b/target/arm/kvm_arm.h
> @@ -207,6 +207,17 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf);
>    */
>   void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
>   
> +/**
> + * kvm_arm_get_max_vm_phys_shift - Returns log2 of the max IPA size
> + * supported by KVM
> + *
> + * @ms: Machine state handle
> + *
> + * Return the max number of IPA bits or a negative value if
> + * the host kernel does not expose this value.
> + */
> +int kvm_arm_get_max_vm_phys_shift(MachineState *ms);
> +
>   /**
>    * kvm_arm_sync_mpstate_to_kvm
>    * @cpu: ARMCPU
> @@ -239,6 +250,11 @@ static inline void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
>       cpu->host_cpu_probe_failed = true;
>   }
>   
> +static inline int kvm_arm_get_max_vm_phys_shift(MachineState *ms)
> +{
> +    return -ENOENT;
> +}
> +
>   static inline int kvm_arm_vgic_probe(void)
>   {
>       return 0;