linux-kernel - Re: [PATCH v3 03/11] KVM: selftests: Test reading a single stat

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Date:   Wed, 6 Apr 2022 13:48:50 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Dunn <daviddunn@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Junaid Shahid <junaids@...gle.com>
Subject: Re: [PATCH v3 03/11] KVM: selftests: Test reading a single stat

On Tue, Apr 5, 2022 at 3:24 PM David Matlack <dmatlack@...gle.com> wrote:
>
> 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@...gle.com>
> > Signed-off-by: Ben Gardon <bgardon@...gle.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.

Will do.

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