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From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-devel@nongnu.org
Cc: Peter Xu <peterx@redhat.com>
Subject: [PULL 18/26] KVM: Disable manual dirty log when dirty ring enabled
Date: Thu, 20 May 2021 10:22:49 +0200	[thread overview]
Message-ID: <20210520082257.187061-19-pbonzini@redhat.com> (raw)
In-Reply-To: <20210520082257.187061-1-pbonzini@redhat.com>

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;
+            }
         }
     }
 
-- 
2.31.1




  parent reply	other threads:[~2021-05-20  8:35 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20  8:22 [PULL 00/26] Misc patches for 2021-05-20 Paolo Bonzini
2021-05-20  8:22 ` [PULL 01/26] configure: Only clone softfloat-3 repositories if TCG is enabled Paolo Bonzini
2021-05-20  8:22 ` [PULL 02/26] configure: check for submodules if --with-git-submodules=ignore Paolo Bonzini
2021-05-20  8:22 ` [PULL 03/26] configure: simplify assignment to GIT_SUBMODULES Paolo Bonzini
2021-05-20  8:22 ` [PULL 04/26] hw/mem/nvdimm: Use Kconfig 'imply' instead of 'depends on' Paolo Bonzini
2021-05-20  8:22 ` [PULL 05/26] i386/cpu: Expose AVX_VNNI instruction to guest Paolo Bonzini
2021-05-20  8:22 ` [PULL 06/26] meson: bump submodule to 0.57.2 Paolo Bonzini
2021-05-20  8:22 ` [PULL 07/26] object: add more commands to preconfig mode Paolo Bonzini
2021-05-20  8:22 ` [PULL 08/26] qtest: add a QOM object for qtest Paolo Bonzini
2021-05-20  8:22 ` [PULL 09/26] KVM: do not allow setting properties at runtime Paolo Bonzini
2021-05-20  8:22 ` [PULL 10/26] memory: Introduce log_sync_global() to memory listener Paolo Bonzini
2021-05-20  8:22 ` [PULL 11/26] KVM: Use a big lock to replace per-kml slots_lock Paolo Bonzini
2021-05-20  8:22 ` [PULL 12/26] KVM: Create the KVMSlot dirty bitmap on flag changes Paolo Bonzini
2021-05-20  8:22 ` [PULL 13/26] KVM: Provide helper to get kvm dirty log Paolo Bonzini
2021-05-20  8:22 ` [PULL 14/26] KVM: Provide helper to sync dirty bitmap from slot to ramblock Paolo Bonzini
2021-05-20  8:22 ` [PULL 15/26] KVM: Simplify dirty log sync in kvm_set_phys_mem Paolo Bonzini
2021-05-20  8:22 ` [PULL 16/26] KVM: Cache kvm slot dirty bitmap size Paolo Bonzini
2021-05-20  8:22 ` [PULL 17/26] KVM: Add dirty-ring-size property Paolo Bonzini
2021-05-20  8:22 ` Paolo Bonzini [this message]
2021-05-20  8:22 ` [PULL 19/26] KVM: Dirty ring support Paolo Bonzini
2021-05-20  8:22 ` [PULL 20/26] tests/qtest/fuzz: Fix build failure Paolo Bonzini
2021-05-20  8:22 ` [PULL 21/26] meson: Set implicit_include_directories to false Paolo Bonzini
2021-05-20  8:22 ` [PULL 22/26] remove qemu-options* from root directory Paolo Bonzini
2021-05-20  8:22 ` [PULL 23/26] replication: move include out of " Paolo Bonzini
2021-05-20  8:22 ` [PULL 24/26] vl: allow not specifying size in -m when using -M memory-backend Paolo Bonzini
2021-05-20  8:22 ` [PULL 25/26] qemu-config: load modules when instantiating option groups Paolo Bonzini
2021-05-20  8:22 ` [PULL 26/26] scsi-generic: pass max_segments via max_iov field in BlockLimits Paolo Bonzini
2021-05-20  8:54 ` [PULL 00/26] Misc patches for 2021-05-20 no-reply
2021-05-20 13:26 ` Peter Maydell
2021-05-20 14:20   ` Peter Maydell
2021-05-20 14:25     ` Peter Maydell
2021-05-21 13:27   ` Paolo Bonzini
2021-05-21 13:44     ` Peter Maydell
2021-05-24  9:42       ` Paolo Bonzini

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