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From:   Paolo Bonzini <pbonzini@redhat.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     vipinsh@google.com, bgardon@google.com, seanjc@google.com
Subject: [PATCH] selftests/kvm: touch all pages of args on each memstress iteration
Date:   Wed, 12 Apr 2023 16:09:13 -0400
Message-Id: <20230412200913.1570873-1-pbonzini@redhat.com>
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Access the same memory addresses on each iteration of the memstress
guest code.  This ensures that the state of KVM's page tables
is the same after every iteration, including the pages that host the
guest page tables for args and vcpu_args.

This difference is visible on the dirty_log_page_splitting_test
on AMD machines.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tools/testing/selftests/kvm/lib/memstress.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kvm/lib/memstress.c b/tools/testing/selftests/kvm/lib/memstress.c
index 3632956c6bcf..df457452d146 100644
--- a/tools/testing/selftests/kvm/lib/memstress.c
+++ b/tools/testing/selftests/kvm/lib/memstress.c
@@ -65,6 +65,9 @@ void memstress_guest_code(uint32_t vcpu_idx)
 	GUEST_ASSERT(vcpu_args->vcpu_idx == vcpu_idx);
 
 	while (true) {
+		for (i = 0; i < sizeof(memstress_args); i += args->guest_page_size)
+			(void) *((volatile char *)args + i);
+
 		for (i = 0; i < pages; i++) {
 			if (args->random_access)
 				page = guest_random_u32(&rand_state) % pages;
-- 
2.39.1