KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is for KVM_CLEAR_DIRTY_LOG, which is only
useful for KVM_GET_DIRTY_LOG. Skip enabling it for kvm dirty ring.
More importantly, KVM_DIRTY_LOG_INITIALLY_SET will not wr-protect all the pages
initially, which is against how kvm dirty ring is used - there's no way for kvm
dirty ring to re-protect a page before it's notified as being written first
with a GFN entry in the ring! So when KVM_DIRTY_LOG_INITIALLY_SET is enabled
with dirty ring, we'll see silent data loss after migration.
Signed-off-by: Peter Xu <pet...@redhat.com>
---
accel/kvm/kvm-all.c | 37 +++++++++++++++++++++++--------------
1 file changed, 23 insertions(+), 14 deletions(-)
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index e438e5d26ad..2404c941784 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2167,20 +2167,29 @@ static int kvm_init(MachineState *ms)
}
}
- dirty_log_manual_caps =
- kvm_check_extension(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
- dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
- KVM_DIRTY_LOG_INITIALLY_SET);
- s->manual_dirty_log_protect = dirty_log_manual_caps;
- if (dirty_log_manual_caps) {
- ret = kvm_vm_enable_cap(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2, 0,
- dirty_log_manual_caps);
- if (ret) {
- warn_report("Trying to enable capability %"PRIu64" of "
- "KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 but failed. "
- "Falling back to the legacy mode. ",
- dirty_log_manual_caps);
- s->manual_dirty_log_protect = 0;
+ /*
+ * KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is not needed when dirty ring is
+ * enabled. More importantly, KVM_DIRTY_LOG_INITIALLY_SET will assume no
+ * page is wr-protected initially, which is against how kvm dirty ring is
+ * usage - kvm dirty ring requires all pages are wr-protected at the very
+ * beginning. Enabling this feature for dirty ring causes data corruption.
+ */
+ if (!s->kvm_dirty_ring_enabled) {
+ dirty_log_manual_caps =
+ kvm_check_extension(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
+ dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
+ KVM_DIRTY_LOG_INITIALLY_SET);
+ s->manual_dirty_log_protect = dirty_log_manual_caps;
+ if (dirty_log_manual_caps) {
+ ret = kvm_vm_enable_cap(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2, 0,
+ dirty_log_manual_caps);
+ if (ret) {
+ warn_report("Trying to enable capability %"PRIu64" of "
+ "KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 but failed. "
+ "Falling back to the legacy mode. ",
+ dirty_log_manual_caps);
+ s->manual_dirty_log_protect = 0;
+ }
}
}
--
2.31.1
