From 07b4b2f4047f600ca7974797900b7409081f826c Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 12 Apr 2023 16:09:13 -0400 Subject: [PATCH] KVM: selftests: touch all pages of args on each memstress iteration 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 when running the proposed dirty_log_page_splitting_test[*] on AMD, or on Intel with pml=0 and eptad=0. The tests fail due to different semantics of dirty bits for page-table pages on AMD (and eptad=0) and Intel. Both AMD and Intel with eptad=0 treat page-table accesses as writes, therefore more pages are dropped before the repopulation phase when dirty logging is disabled. The "missing" page had been included in the population phase because it hosts the page tables for vcpu_args, but repopulation does not need it." Signed-off-by: Paolo Bonzini Reviewed-by: Vipin Sharma Link: https://lore.kernel.org/r/20230412200913.1570873-1-pbonzini@redhat.com [sean: add additional details in changelog] Signed-off-by: Sean Christopherson --- 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 5f1d3173c238c..7d2f812e7c9ae 100644 --- a/tools/testing/selftests/kvm/lib/memstress.c +++ b/tools/testing/selftests/kvm/lib/memstress.c @@ -64,6 +64,9 @@ 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; -- 2.30.2