linux-kernel - Re: [PATCH v4 12/18] KVM: selftests: Keep track of the number of vCPUs for a VM

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Date:   Thu, 9 Sep 2021 15:20:19 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Peter Shier <pshier@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 12/18] KVM: selftests: Keep track of the number of
 vCPUs for a VM

On Thu, Sep 09, 2021 at 01:38:12AM +0000, Raghavendra Rao Ananta wrote:
> The host may want to know the number of vCPUs that were
> created for a particular VM (used in upcoming patches).
> Hence, include nr_vcpus as a part of 'struct kvm_vm' to
> keep track of vCPUs as and when they are added or
> deleted, and return to the caller via vm_get_nr_vcpus().
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> ---
>  tools/testing/selftests/kvm/include/kvm_util.h      | 1 +
>  tools/testing/selftests/kvm/lib/kvm_util.c          | 7 +++++++
>  tools/testing/selftests/kvm/lib/kvm_util_internal.h | 1 +
>  3 files changed, 9 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 010b59b13917..d5d0ca919928 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -399,5 +399,6 @@ uint64_t get_ucall(struct kvm_vm *vm, uint32_t vcpu_id, struct ucall *uc);
>  
>  int vm_get_stats_fd(struct kvm_vm *vm);
>  int vcpu_get_stats_fd(struct kvm_vm *vm, uint32_t vcpuid);
> +int vm_get_nr_vcpus(struct kvm_vm *vm);
>  
>  #endif /* SELFTEST_KVM_UTIL_H */
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 10a8ed691c66..1b5349b5132f 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -594,6 +594,7 @@ static void vm_vcpu_rm(struct kvm_vm *vm, struct vcpu *vcpu)
>  
>  	list_del(&vcpu->list);
>  	free(vcpu);
> +	vm->nr_vcpus--;
>  }
>  
>  void kvm_vm_release(struct kvm_vm *vmp)
> @@ -1143,6 +1144,7 @@ void vm_vcpu_add(struct kvm_vm *vm, uint32_t vcpuid)
>  
>  	/* Add to linked-list of VCPUs. */
>  	list_add(&vcpu->list, &vm->vcpus);
> +	vm->nr_vcpus++;
>  }
>  
>  /*
> @@ -2343,3 +2345,8 @@ int vcpu_get_stats_fd(struct kvm_vm *vm, uint32_t vcpuid)
>  
>  	return ioctl(vcpu->fd, KVM_GET_STATS_FD, NULL);
>  }
> +
> +int vm_get_nr_vcpus(struct kvm_vm *vm)
> +{
> +	return vm->nr_vcpus;
> +}

nr_vcpus looks like useful library internal information, since the only
other way to get the number is to iterate the vcpu list. I'm not sure
if we need this vm_get_nr_vcpus() accessor for tests yet though. Maybe
it'll be more clear to me when I see how it's used.

Thanks,
drew

> diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h
> index a03febc24ba6..be4d852d2f3b 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h
> +++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h
> @@ -56,6 +56,7 @@ struct kvm_vm {
>  	unsigned int va_bits;
>  	uint64_t max_gfn;
>  	struct list_head vcpus;
> +	int nr_vcpus;
>  	struct userspace_mem_regions regions;
>  	struct sparsebit *vpages_valid;
>  	struct sparsebit *vpages_mapped;
> -- 
> 2.33.0.153.gba50c8fa24-goog
>