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Date:   Tue, 5 Apr 2022 22:24:12 +0000
From:   David Matlack <dmatlack@google.com>
To:     Ben Gardon <bgardon@google.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Jim Mattson <jmattson@google.com>,
        David Dunn <daviddunn@google.com>,
        Jing Zhang <jingzhangos@google.com>,
        Junaid Shahid <junaids@google.com>
Subject: Re: [PATCH v3 03/11] KVM: selftests: Test reading a single stat
Message-ID: <YkzBjF3NyI9fyZad@google.com>
References: <20220330174621.1567317-1-bgardon@google.com>
 <20220330174621.1567317-4-bgardon@google.com>
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On Wed, Mar 30, 2022 at 10:46:13AM -0700, Ben Gardon wrote:
> Retrieve the value of a single stat by name in the binary stats test to
> ensure the kvm_util library functions work.
> 
> CC: Jing Zhang <jingzhangos@google.com>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>  .../selftests/kvm/include/kvm_util_base.h     |  1 +
>  .../selftests/kvm/kvm_binary_stats_test.c     |  3 ++
>  tools/testing/selftests/kvm/lib/kvm_util.c    | 53 +++++++++++++++++++
>  3 files changed, 57 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index 4783fd1cd4cf..78c4407f36b4 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -402,6 +402,7 @@ void assert_on_unhandled_exception(struct kvm_vm *vm, uint32_t vcpuid);
>  int vm_get_stats_fd(struct kvm_vm *vm);
>  int vcpu_get_stats_fd(struct kvm_vm *vm, uint32_t vcpuid);
>  void dump_vm_stats(struct kvm_vm *vm);
> +uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name);
>  
>  uint32_t guest_get_vcpuid(void);
>  
> diff --git a/tools/testing/selftests/kvm/kvm_binary_stats_test.c b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> index afc4701ce8dd..97bde355f105 100644
> --- a/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> +++ b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> @@ -177,6 +177,9 @@ static void vm_stats_test(struct kvm_vm *vm)
>  
>  	/* Dump VM stats */
>  	dump_vm_stats(vm);
> +
> +	/* Read a single stat. */
> +	printf("remote_tlb_flush: %lu\n", vm_get_single_stat(vm, "remote_tlb_flush"));
>  }
>  
>  static void vcpu_stats_test(struct kvm_vm *vm, int vcpu_id)
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index f87df68b150d..9c4574381daa 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -2705,3 +2705,56 @@ void dump_vm_stats(struct kvm_vm *vm)
>  	close(stats_fd);
>  }
>  
> +static int vm_get_stat_data(struct kvm_vm *vm, const char *stat_name,
> +			    uint64_t **data)
> +{
> +	struct kvm_stats_desc *stats_desc;
> +	struct kvm_stats_header *header;
> +	struct kvm_stats_desc *desc;
> +	size_t size_desc;
> +	int stats_fd;
> +	int ret = -EINVAL;
> +	int i;
> +
> +	*data = NULL;
> +
> +	stats_fd = vm_get_stats_fd(vm);
> +
> +	header = read_vm_stats_header(stats_fd);
> +
> +	stats_desc = read_vm_stats_desc(stats_fd, header);
> +
> +	size_desc = stats_desc_size(header);
> +
> +	/* Read kvm stats data one by one */
> +	for (i = 0; i < header->num_desc; ++i) {
> +		desc = (void *)stats_desc + (i * size_desc);
> +
> +		if (strcmp(desc->name, stat_name))
> +			continue;
> +
> +		ret = read_stat_data(stats_fd, header, desc, data);
> +	}
> +
> +	free(stats_desc);
> +	free(header);
> +
> +	close(stats_fd);
> +
> +	return ret;
> +}
> +
> +uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name)
> +{
> +	uint64_t *data;
> +	uint64_t value;
> +	int ret;
> +
> +	ret = vm_get_stat_data(vm, stat_name, &data);
> +	TEST_ASSERT(ret == 1, "Stat %s expected to have 1 element, but has %d",
> +		    stat_name, ret);
> +	value = *data;
> +	free(data);

Allocating temporary storage for the data is unnecessary. Just read the
stat directly into &value. You'll need to change read_stat_data() to
accept another parameter that defines the number of elements the caller
wants to read. Otherwise botched stats could trigger a buffer overflow.

> +	return value;
> +}
> +
> -- 
> 2.35.1.1021.g381101b075-goog
>