KVM: x86: enable dirty log gradually in small chunks

mainline inclusion
from mainline-v5.10
commit: 3c9bd400
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I66COX
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=3c9bd4006bfc2dccda1823db61b3f470ef91cfaa



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It could take kvm->mmu_lock for an extended period of time when
enabling dirty log for the first time. The main cost is to clear
all the D-bits of last level SPTEs. This situation can benefit from
manual dirty log protect as well, which can reduce the mmu_lock
time taken. The sequence is like this:

1. Initialize all the bits of the dirty bitmap to 1 when enabling
   dirty log for the first time
2. Only write protect the huge pages
3. KVM_GET_DIRTY_LOG returns the dirty bitmap info
4. KVM_CLEAR_DIRTY_LOG will clear D-bit for each of the leaf level
   SPTEs gradually in small chunks

Under the Intel(R) Xeon(R) Gold 6152 CPU @ 2.10GHz environment,
I did some tests with a 128G windows VM and counted the time taken
of memory_global_dirty_log_start, here is the numbers:

VM Size        Before    After optimization
128G           460ms     10ms

Signed-off-by: Jay Zhou <jianjay.zhou@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[Remove test code because the test code is too different.]
Signed-off-by:  <zhengchuan&lt;zhengchuan@huawei.com>