From: Zhuang Yanying <ann.zhuangyany...@huawei.com>
When live-migration with large-memory guests, vcpu may hang for a long
time while starting migration, such as 9s for 2T
(linux-5.0.0-rc2+qemu-3.1.0).
The reason is memory_global_dirty_log_start() taking too long, and the
vcpu is waiting for BQL. The page-by-page D bit clearup is the main time
consumption. I think that the idea of "KVM: MMU: fast write protect" by
xiaoguangrong, especially the function kvm_mmu_write_protect_all_pages(),
is very helpful. After a little modifcation, on his patch, can solve
this problem, 9s to 0.5s.
At the beginning of live migration, write protection is only applied to the
top-level SPTE. Then the write from vm trigger the EPT violation, with
for_each_shadow_entry write protection is performed at dirct_map.
Finally the Dirty bit of the target page(at level 1 page table) is
cleared, and the dirty page tracking is started. The page where
GPA is located is marked dirty when mmu_set_spte.
Signed-off-by: Zhuang Yanying <ann.zhuangyany...@huawei.com>
---
arch/x86/kvm/mmu.c | 6 +++++-
arch/x86/kvm/vmx/vmx.c | 5 ++---
2 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index effae7a..ac7a994 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3230,7 +3230,10 @@ static bool mmu_load_shadow_page(struct kvm *kvm, struct
kvm_mmu_page *sp)
break;
if (is_last_spte(spte, sp->role.level)) {
- flush |= spte_write_protect(sptep, false);
+ if (sp->role.level == PT_PAGE_TABLE_LEVEL)
+ flush |= spte_clear_dirty(sptep);
+ else
+ flush |= spte_write_protect(sptep, false);
continue;
}
@@ -6106,6 +6109,7 @@ void kvm_mmu_write_protect_all_pages(struct kvm *kvm,
bool write_protect)
kvm_reload_remote_mmus(kvm);
spin_unlock(&kvm->mmu_lock);
}
+EXPORT_SYMBOL_GPL(kvm_mmu_write_protect_all_pages);
static unsigned long
mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f6915f1..540ec21 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7180,14 +7180,13 @@ static void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu)
static void vmx_slot_enable_log_dirty(struct kvm *kvm,
struct kvm_memory_slot *slot)
{
- kvm_mmu_slot_leaf_clear_dirty(kvm, slot);
- kvm_mmu_slot_largepage_remove_write_access(kvm, slot);
+ kvm_mmu_write_protect_all_pages(kvm, true);
}
static void vmx_slot_disable_log_dirty(struct kvm *kvm,
struct kvm_memory_slot *slot)
{
- kvm_mmu_slot_set_dirty(kvm, slot);
+ kvm_mmu_write_protect_all_pages(kvm, false);
}
static void vmx_flush_log_dirty(struct kvm *kvm)
--
1.8.3.1
