On Mon, Jan 21, 2019 at 06:37:36AM +0000, Zhuangyanying wrote: > > > > u64 wp_all_indicator, kvm_wp_all_gen; > > > > > > - mutex_lock(&kvm->slots_lock); > > > wp_all_indicator = get_write_protect_all_indicator(kvm); > > > kvm_wp_all_gen = get_write_protect_all_gen(wp_all_indicator); > > > > > > @@ -6134,8 +6136,8 @@ void kvm_mmu_write_protect_all_pages(struct > > kvm *kvm, bool write_protect) > > > */ > > > if (write_protect) > > > kvm_reload_remote_mmus(kvm); > > > - mutex_unlock(&kvm->slots_lock); > > > > Why is the lock removed? And why was it added in the first place? > > > The original purpose of fast write protect is to implement lock-free get_dirty_log, > kvm_mmu_write_protect_all_pages is a stand-alone kvm API. See > https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg04370.html > A total of 7 patches, I only need the first 3 patches to achieve step-by-step > page table traversal. In order to maintain the integrity of the xiaoguangrong > patch, I did not directly modify it on his patch. That's not a sufficient argument for adding locking and removing it one patch later. > > > } > > > +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..5236a07 100644 > > > --- a/arch/x86/kvm/vmx/vmx.c > > > +++ b/arch/x86/kvm/vmx/vmx.c > > > @@ -7180,8 +7180,7 @@ 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); > > > > What's the purpose of having @write_protect if > > kvm_mmu_write_protect_all_pages() is only ever called to enable > > protection? If there's no known scenario where write protection is > > explicitly disabled then there's no need for WP_ALL_ENABLE_MASK, i.e. a > > non-zero generation would indicate write protection is enabled. That'd > > simplify the code and clean up the atomic usage. > > > In the live migration, The large page split depends on the creation of memslot->dirty_bitmap > in the function __kvm_set_memory_region(). > The interface design between qemu and kvm to enable dirty log is one by one in slot units. > In order to enable dirty page tracking of the entire vm, it is necessary to call > kvm_mmu_write_protect_all_pages multiple times. The page table update request can > be merged for processing by the atomic usage. This method is not elegant, but it works. > Complete the creation of all solt's dirty_bitmap in an API, just call > kvm_mmu_write_protect_all_pages once, need more implementation changes, even qemu. Calling kvm_mmu_write_protect_all_pages() multiple times is fine. My question was regarding the 'write_protect' parameter. If all callers always pass %true for 'write_protect' then why does the parameter exist? And eliminating the parameter means you don't need an 'enable' flag buried in the generation, which would simplify the implementation.
