KVM: x86: enable dirty log gradually in small chunks
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>
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@ -5707,8 +5707,13 @@ and injected exceptions.
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:Architectures: x86, arm, arm64, mips
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:Parameters: args[0] whether feature should be enabled or not
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With this capability enabled, KVM_GET_DIRTY_LOG will not automatically
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clear and write-protect all pages that are returned as dirty.
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Valid flags are::
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#define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (1 << 0)
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#define KVM_DIRTY_LOG_INITIALLY_SET (1 << 1)
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With KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE is set, KVM_GET_DIRTY_LOG will not
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automatically clear and write-protect all pages that are returned as dirty.
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Rather, userspace will have to do this operation separately using
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KVM_CLEAR_DIRTY_LOG.
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@ -5719,12 +5724,19 @@ than requiring to sync a full memslot; this ensures that KVM does not
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take spinlocks for an extended period of time. Second, in some cases a
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large amount of time can pass between a call to KVM_GET_DIRTY_LOG and
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userspace actually using the data in the page. Pages can be modified
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during this time, which is inefficint for both the guest and userspace:
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during this time, which is inefficient for both the guest and userspace:
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the guest will incur a higher penalty due to write protection faults,
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while userspace can see false reports of dirty pages. Manual reprotection
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helps reducing this time, improving guest performance and reducing the
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number of dirty log false positives.
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With KVM_DIRTY_LOG_INITIALLY_SET set, all the bits of the dirty bitmap
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will be initialized to 1 when created. This also improves performance because
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dirty logging can be enabled gradually in small chunks on the first call
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to KVM_CLEAR_DIRTY_LOG. KVM_DIRTY_LOG_INITIALLY_SET depends on
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KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (it is also only available on
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x86 for now).
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KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name
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KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make
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it hard or impossible to use it correctly. The availability of
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@ -49,6 +49,9 @@
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#define KVM_IRQCHIP_NUM_PINS KVM_IOAPIC_NUM_PINS
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#define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
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KVM_DIRTY_LOG_INITIALLY_SET)
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/* x86-specific vcpu->requests bit members */
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#define KVM_REQ_MIGRATE_TIMER KVM_ARCH_REQ(0)
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#define KVM_REQ_REPORT_TPR_ACCESS KVM_ARCH_REQ(1)
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@ -1306,7 +1309,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
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void kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
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void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
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struct kvm_memory_slot *memslot);
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struct kvm_memory_slot *memslot,
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int start_level);
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void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
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const struct kvm_memory_slot *memslot);
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void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
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@ -5864,13 +5864,14 @@ static bool slot_rmap_write_protect(struct kvm *kvm,
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}
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void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
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struct kvm_memory_slot *memslot)
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struct kvm_memory_slot *memslot,
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int start_level)
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{
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bool flush;
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spin_lock(&kvm->mmu_lock);
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flush = slot_handle_all_level(kvm, memslot, slot_rmap_write_protect,
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false);
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flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
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start_level, PT_MAX_HUGEPAGE_LEVEL, false);
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spin_unlock(&kvm->mmu_lock);
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/*
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@ -7280,7 +7280,8 @@ static void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu)
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static void vmx_slot_enable_log_dirty(struct kvm *kvm,
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struct kvm_memory_slot *slot)
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{
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kvm_mmu_slot_leaf_clear_dirty(kvm, slot);
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if (!kvm_dirty_log_manual_protect_and_init_set(kvm))
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kvm_mmu_slot_leaf_clear_dirty(kvm, slot);
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kvm_mmu_slot_largepage_remove_write_access(kvm, slot);
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}
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@ -9916,7 +9916,7 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
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{
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/* Still write protect RO slot */
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if (new->flags & KVM_MEM_READONLY) {
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kvm_mmu_slot_remove_write_access(kvm, new);
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kvm_mmu_slot_remove_write_access(kvm, new, PT_PAGE_TABLE_LEVEL);
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return;
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}
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@ -9951,10 +9951,23 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
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* See the comments in fast_page_fault().
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*/
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if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
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if (kvm_x86_ops->slot_enable_log_dirty)
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if (kvm_x86_ops->slot_enable_log_dirty) {
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kvm_x86_ops->slot_enable_log_dirty(kvm, new);
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else
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kvm_mmu_slot_remove_write_access(kvm, new);
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} else {
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int level =
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kvm_dirty_log_manual_protect_and_init_set(kvm) ?
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PT_DIRECTORY_LEVEL : PT_PAGE_TABLE_LEVEL;
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/*
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* If we're with initial-all-set, we don't need
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* to write protect any small page because
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* they're reported as dirty already. However
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* we still need to write-protect huge pages
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* so that the page split can happen lazily on
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* the first write to the huge page.
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*/
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kvm_mmu_slot_remove_write_access(kvm, new, level);
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}
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} else {
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if (kvm_x86_ops->slot_disable_log_dirty)
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kvm_x86_ops->slot_disable_log_dirty(kvm, new);
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@ -360,6 +360,10 @@ static inline unsigned long *kvm_second_dirty_bitmap(struct kvm_memory_slot *mem
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return memslot->dirty_bitmap + len / sizeof(*memslot->dirty_bitmap);
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}
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#ifndef KVM_DIRTY_LOG_MANUAL_CAPS
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#define KVM_DIRTY_LOG_MANUAL_CAPS KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE
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#endif
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struct kvm_s390_adapter_int {
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u64 ind_addr;
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u64 summary_addr;
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@ -493,7 +497,7 @@ struct kvm {
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#endif
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long tlbs_dirty;
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struct list_head devices;
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bool manual_dirty_log_protect;
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u64 manual_dirty_log_protect;
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struct dentry *debugfs_dentry;
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struct kvm_stat_data **debugfs_stat_data;
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struct srcu_struct srcu;
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@ -527,6 +531,11 @@ struct kvm {
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#define vcpu_err(vcpu, fmt, ...) \
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kvm_err("vcpu%i " fmt, (vcpu)->vcpu_id, ## __VA_ARGS__)
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static inline bool kvm_dirty_log_manual_protect_and_init_set(struct kvm *kvm)
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{
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return !!(kvm->manual_dirty_log_protect & KVM_DIRTY_LOG_INITIALLY_SET);
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}
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static inline struct kvm_io_bus *kvm_get_bus(struct kvm *kvm, enum kvm_bus idx)
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{
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return srcu_dereference_check(kvm->buses[idx], &kvm->srcu,
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@ -1628,4 +1628,7 @@ struct kvm_hyperv_eventfd {
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#define KVM_HYPERV_CONN_ID_MASK 0x00ffffff
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#define KVM_HYPERV_EVENTFD_DEASSIGN (1 << 0)
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#define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (1 << 0)
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#define KVM_DIRTY_LOG_INITIALLY_SET (1 << 1)
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#endif /* __LINUX_KVM_H */
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@ -858,7 +858,7 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
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* Allocation size is twice as large as the actual dirty bitmap size.
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* See kvm_vm_ioctl_get_dirty_log() why this is needed.
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*/
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static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
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static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot)
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{
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unsigned long dirty_bytes = 2 * kvm_dirty_bitmap_bytes(memslot);
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if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
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new.dirty_bitmap = NULL;
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else if (!new.dirty_bitmap) {
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r = kvm_create_dirty_bitmap(&new);
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r = kvm_alloc_dirty_bitmap(&new);
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if (r)
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return r;
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if (kvm_dirty_log_manual_protect_and_init_set(kvm))
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bitmap_set(new.dirty_bitmap, 0, new.npages);
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}
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r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
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case KVM_CAP_IOEVENTFD_ANY_LENGTH:
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case KVM_CAP_CHECK_EXTENSION_VM:
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case KVM_CAP_ENABLE_CAP_VM:
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#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
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case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2:
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#endif
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return 1;
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#ifdef CONFIG_KVM_MMIO
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case KVM_CAP_COALESCED_MMIO:
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case KVM_CAP_COALESCED_PIO:
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return 1;
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#endif
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#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
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case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2:
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return KVM_DIRTY_LOG_MANUAL_CAPS;
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#endif
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#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
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case KVM_CAP_IRQ_ROUTING:
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return KVM_MAX_IRQ_ROUTES;
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{
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switch (cap->cap) {
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#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
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case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2:
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if (cap->flags || (cap->args[0] & ~1))
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case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2: {
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u64 allowed_options = KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE;
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if (cap->args[0] & KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE)
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allowed_options = KVM_DIRTY_LOG_MANUAL_CAPS;
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if (cap->flags || (cap->args[0] & ~allowed_options))
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return -EINVAL;
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kvm->manual_dirty_log_protect = cap->args[0];
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return 0;
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}
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#endif
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default:
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return kvm_vm_ioctl_enable_cap(kvm, cap);
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