Re: [PATCH v3 05/16] KVM: selftests: Add helper to generate random u64 in range [min,max]

[Sean Christopherson]

On Tue, Apr 21, 2026, Josh Hilke wrote:
> Introduce kvm_random_u64_in_range(state, min, max). This function
> returns a random u64 in the inclusive range of [min, max] using a struct
> kvm_random_state.
> 
> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Josh Hilke <jrhilke@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/include/test_util.h |  4 ++++
>  tools/testing/selftests/kvm/lib/test_util.c     | 16 ++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> index ae39c4293b9a..584a4ab43db5 100644
> --- a/tools/testing/selftests/kvm/include/test_util.h
> +++ b/tools/testing/selftests/kvm/include/test_util.h
> @@ -132,6 +132,10 @@ static inline uint64_t kvm_random_u64(struct kvm_random_state *state)
>  	return ((uint64_t)kvm_random_u32(state) << 32) | kvm_random_u32(state);
>  }
>  
> +/* Returns a random u64 in the inclusive range [min, max] */

Put the comment above the definition (But thank you for writing it!  I had typed
up a response asking for exactly this, before I realized it was there, just on
the declaration).

> +uint64_t kvm_random_u64_in_range(struct kvm_random_state *state, uint64_t min,
> +				 uint64_t max);
> +
>  enum vm_mem_backing_src_type {
>  	VM_MEM_SRC_ANONYMOUS,
>  	VM_MEM_SRC_ANONYMOUS_THP,
> diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> index e342d9fb4771..23d543a9053e 100644
> --- a/tools/testing/selftests/kvm/lib/test_util.c
> +++ b/tools/testing/selftests/kvm/lib/test_util.c
> @@ -42,6 +42,22 @@ uint32_t kvm_random_u32(struct kvm_random_state *state)
>  	return state->seed;
>  }
>  
> +uint64_t kvm_random_u64_in_range(struct kvm_random_state *state, uint64_t min, uint64_t max)

Wrap.

> +{
> +	uint64_t value;
> +	uint64_t range;
> +
> +	TEST_ASSERT(min <= max, "min (0x%lx) cannot be greater than max (0x%lx)", min, max);

LOL, that's a rather hilarious error message.  Partly because it's so pointless
(gotta love TEST_ASSERT()), partly because @min obviously _can_ be greater than
@max :-)

The "min <= max" that gets printed is pretty darn self-explanatory, maybe take
the opportunity to throw shade at the user/developer?

	TEST_ASSERT(min <= max, "PEBKAC, min = 0x%lx, max = 0x%lx", min, max);

> +
> +	value = kvm_random_u64(state);
> +
> +	range = max - min;
> +	if (range == ULLONG_MAX)
> +		return value;
> +
> +	return min + (value % (range + 1));
> +}
> +
>  /*
>   * Parses "[0-9]+[kmgt]?".
>   */
> -- 
> 2.54.0.rc2.533.g4f5dca5207-goog
>