From: Keqian Zhu <zhukeqian1@huawei.com>
To: Peter Xu <peterx@redhat.com>, <qemu-devel@nongnu.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Hyman <huangy81@chinatelecom.cn>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v5 09/10] KVM: Disable manual dirty log when dirty ring enabled
Date: Mon, 22 Mar 2021 17:17:47 +0800 [thread overview]
Message-ID: <c49abf47-412c-26b8-0a28-c1007eed0159@huawei.com> (raw)
In-Reply-To: <20210310203301.194842-10-peterx@redhat.com>
Hi Peter,
On 2021/3/11 4:33, Peter Xu wrote:
> 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.
I feel a little regret that dirty ring can not work with KVM_DIRTY_LOG_INITIALLY_SET ...
With KVM_DIRTY_LOG_INITIALLY_SET, we can speedup dirty log start. More important, we can
enable dirty log gradually. For write fault based dirty log, it greatly reduces the side
effect of dirty log over guest.
I hope we can put forward another similar optimization under dirty ring mode. :)
Thanks,
Keqian
>
> Signed-off-by: Peter Xu <peterx@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 10137b6af11..ae9393266b2 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2173,20 +2173,29 @@ 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;
> + }
> }
> }
>
>
next prev parent reply other threads:[~2021-03-22 9:19 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 20:32 [PATCH v5 00/10] KVM: Dirty ring support (QEMU part) Peter Xu
2021-03-10 20:32 ` [PATCH v5 01/10] memory: Introduce log_sync_global() to memory listener Peter Xu
2021-03-10 20:32 ` [PATCH v5 02/10] KVM: Use a big lock to replace per-kml slots_lock Peter Xu
2021-03-22 10:47 ` Keqian Zhu
2021-03-22 13:54 ` Paolo Bonzini
2021-03-22 16:27 ` Peter Xu
2021-03-24 18:08 ` Peter Xu
2021-03-10 20:32 ` [PATCH v5 03/10] KVM: Create the KVMSlot dirty bitmap on flag changes Peter Xu
2021-03-10 20:32 ` [PATCH v5 04/10] KVM: Provide helper to get kvm dirty log Peter Xu
2021-03-10 20:32 ` [PATCH v5 05/10] KVM: Provide helper to sync dirty bitmap from slot to ramblock Peter Xu
2021-03-10 20:32 ` [PATCH v5 06/10] KVM: Simplify dirty log sync in kvm_set_phys_mem Peter Xu
2021-03-10 20:32 ` [PATCH v5 07/10] KVM: Cache kvm slot dirty bitmap size Peter Xu
2021-03-10 20:32 ` [PATCH v5 08/10] KVM: Add dirty-gfn-count property Peter Xu
2021-03-10 20:33 ` [PATCH v5 09/10] KVM: Disable manual dirty log when dirty ring enabled Peter Xu
2021-03-22 9:17 ` Keqian Zhu [this message]
2021-03-22 13:55 ` Paolo Bonzini
2021-03-22 16:21 ` Peter Xu
2021-03-10 20:33 ` [PATCH v5 10/10] KVM: Dirty ring support Peter Xu
2021-03-22 13:37 ` Keqian Zhu
2021-03-22 18:52 ` Peter Xu
2021-03-23 1:25 ` Keqian Zhu
2021-03-19 18:12 ` [PATCH v5 00/10] KVM: Dirty ring support (QEMU part) Peter Xu
2021-03-22 14:02 ` Keqian Zhu
2021-03-22 19:45 ` Peter Xu
2021-03-23 6:40 ` Keqian Zhu
2021-03-23 14:34 ` Peter Xu
2021-03-24 2:56 ` Keqian Zhu
2021-03-24 15:09 ` Peter Xu
2021-03-25 1:21 ` Keqian Zhu
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