Re: [PATCH] KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()

[Peter Xu <peterx@redhat.com>]

On Thu, May 20, 2021 at 09:26:54PM +0000, David Matlack wrote:
> vm_get_max_gfn() casts vm->max_gfn from a uint64_t to an unsigned int,
> which causes the upper 32-bits of the max_gfn to get truncated.
> 
> Nobody noticed until now likely because vm_get_max_gfn() is only used
> as a mechanism to create a memslot in an unused region of the guest
> physical address space (the top), and the top of the 32-bit physical
> address space was always good enough.

s/top/bottom/?

Looks right.. thanks for fixing it!

> 
> This fix reveals a bug in memslot_modification_stress_test which was
> trying to create a dummy memslot past the end of guest physical memory.
> Fix that by moving the dummy memslot lower.

Would it be better to split the different fixes?

> 
> Fixes: 52200d0d944e ("KVM: selftests: Remove duplicate guest mode handling")
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>  tools/testing/selftests/kvm/include/kvm_util.h |  2 +-
>  tools/testing/selftests/kvm/lib/kvm_util.c     |  2 +-
>  .../testing/selftests/kvm/lib/perf_test_util.c |  2 +-
>  .../kvm/memslot_modification_stress_test.c     | 18 +++++++++++-------
>  4 files changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 84982eb02b29..5d9b35d09251 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -303,7 +303,7 @@ bool vm_is_unrestricted_guest(struct kvm_vm *vm);
>  
>  unsigned int vm_get_page_size(struct kvm_vm *vm);
>  unsigned int vm_get_page_shift(struct kvm_vm *vm);
> -unsigned int vm_get_max_gfn(struct kvm_vm *vm);
> +uint64_t vm_get_max_gfn(struct kvm_vm *vm);
>  int vm_get_fd(struct kvm_vm *vm);
>  
>  unsigned int vm_calc_num_guest_pages(enum vm_guest_mode mode, size_t size);
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 1af1009254c4..aeffbb1e7c7d 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -2058,7 +2058,7 @@ unsigned int vm_get_page_shift(struct kvm_vm *vm)
>  	return vm->page_shift;
>  }
>  
> -unsigned int vm_get_max_gfn(struct kvm_vm *vm)
> +uint64_t vm_get_max_gfn(struct kvm_vm *vm)
>  {
>  	return vm->max_gfn;
>  }
> diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
> index 81490b9b4e32..ed4424ed26d6 100644
> --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> @@ -80,7 +80,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
>  	 */
>  	TEST_ASSERT(guest_num_pages < vm_get_max_gfn(vm),
>  		    "Requested more guest memory than address space allows.\n"
> -		    "    guest pages: %lx max gfn: %x vcpus: %d wss: %lx]\n",
> +		    "    guest pages: %lx max gfn: %lx vcpus: %d wss: %lx]\n",

If to fix it, maybe start to use PRIu64 (and include inttypes.h)?

Thanks,

-- 
Peter Xu