Re: [PATCH v8 40/46] KVM: selftests: Reset shared memory after hole-punching

[Fuad Tabba <tabba@google.com>]

On Fri, 19 Jun 2026 at 01:32, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@kernel.org> wrote:
>
> From: Ackerley Tng <ackerleytng@google.com>
>
> private_mem_conversions_test used to reset the shared memory that was used
> for the test to an initial pattern at the end of each test iteration. Then,
> it would punch out the pages, which would zero memory.
>
> Without in-place conversion, the resetting would write shared memory, and
> hole-punching will zero private memory, hence resetting the test to the
> state at the beginning of the for loop.
>
> With in-place conversion, resetting writes memory as shared, and
> hole-punching zeroes the same physical memory, hence undoing the reset
> done before the hole punch.
>
> Move the resetting after the hole-punching, and reset the entire
> PER_CPU_DATA_SIZE instead of just the tested range.
>
> With in-place conversion, this zeroes and then resets the same physical
> memory. Without in-place conversion, the private memory is zeroed, and the
> shared memory is reset to init_p.
>
> This is sufficient since at each test stage, the memory is assumed to start
> as shared, and private memory is always assumed to start zeroed. Conversion
> zeroes memory, so the future test stages will work as expected.
>
> Fixes: 43f623f350ce1 ("KVM: selftests: Add x86-only selftest for private memory conversions")
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>

Reviewed-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad

> ---
>  tools/testing/selftests/kvm/x86/private_mem_conversions_test.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
> index 861baff201e78..289ad10063fca 100644
> --- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
> +++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
> @@ -202,15 +202,18 @@ static void guest_test_explicit_conversion(u64 base_gpa, bool do_fallocate)
>                 guest_sync_shared(gpa, size, p3, p4);
>                 memcmp_g(gpa, p4, size);
>
> -               /* Reset the shared memory back to the initial pattern. */
> -               memset((void *)gpa, init_p, size);
> -
>                 /*
>                  * Free (via PUNCH_HOLE) *all* private memory so that the next
>                  * iteration starts from a clean slate, e.g. with respect to
>                  * whether or not there are pages/folios in guest_mem.
>                  */
>                 guest_map_shared(base_gpa, PER_CPU_DATA_SIZE, true);
> +
> +               /*
> +                * Hole-punching above zeroed private memory. Reset shared
> +                * memory in preparation for the next GUEST_STAGE.
> +                */
> +               memset((void *)base_gpa, init_p, PER_CPU_DATA_SIZE);
>         }
>  }
>
>
> --
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>
>