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[PULL 19/20] KVM: Disable manual dirty log when dirty ring enabled
From: |
Paolo Bonzini |
Subject: |
[PULL 19/20] KVM: Disable manual dirty log when dirty ring enabled |
Date: |
Mon, 17 May 2021 07:20:00 -0400 |
From: Peter Xu <peterx@redhat.com>
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 <peterx@redhat.com>
Message-Id: <20210506160549.130416-10-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@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 5afe15ae66..e1a6c7c89b 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2131,20 +2131,29 @@ static int kvm_init(MachineState *ms)
s->coalesced_pio = s->coalesced_mmio &&
kvm_check_extension(s, KVM_CAP_COALESCED_PIO);
- 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_size) {
+ 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;
+ }
}
}
--
2.27.0
- [PULL 09/20] qtest: add a QOM object for qtest, (continued)
- [PULL 09/20] qtest: add a QOM object for qtest, Paolo Bonzini, 2021/05/17
- [PULL 06/20] i386/cpu: Expose AVX_VNNI instruction to guest, Paolo Bonzini, 2021/05/17
- [PULL 11/20] memory: Introduce log_sync_global() to memory listener, Paolo Bonzini, 2021/05/17
- [PULL 12/20] KVM: Use a big lock to replace per-kml slots_lock, Paolo Bonzini, 2021/05/17
- [PULL 13/20] KVM: Create the KVMSlot dirty bitmap on flag changes, Paolo Bonzini, 2021/05/17
- [PULL 14/20] KVM: Provide helper to get kvm dirty log, Paolo Bonzini, 2021/05/17
- [PULL 15/20] KVM: Provide helper to sync dirty bitmap from slot to ramblock, Paolo Bonzini, 2021/05/17
- [PULL 16/20] KVM: Simplify dirty log sync in kvm_set_phys_mem, Paolo Bonzini, 2021/05/17
- [PULL 18/20] KVM: Add dirty-ring-size property, Paolo Bonzini, 2021/05/17
- [PULL 17/20] KVM: Cache kvm slot dirty bitmap size, Paolo Bonzini, 2021/05/17
- [PULL 19/20] KVM: Disable manual dirty log when dirty ring enabled,
Paolo Bonzini <=
- [PULL 20/20] KVM: Dirty ring support, Paolo Bonzini, 2021/05/17
- Re: [PULL 00/20] Misc patches for 2020-05-17, no-reply, 2021/05/17
- Re: [PULL 00/20] Misc patches for 2020-05-17, Peter Maydell, 2021/05/18