[RFC PATCH v2 29/37] KVM: selftests: Reset shared memory after hole-punching

[Ackerley Tng]

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 <ackerley...@google.com>
---
 .../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 41f6b38f0407..47f1eb921259 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(uint64_t 
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);
        }
 }
 
-- 
2.53.0.rc1.225.gd81095ad13-goog