> -----Original Message----- > From: Peter Xu [mailto:peterx@xxxxxxxxxx] > Sent: Tuesday, February 25, 2020 1:06 AM > To: Zhoujian (jay) <jianjay.zhou@xxxxxxxxxx> > Cc: kvm@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; > sean.j.christopherson@xxxxxxxxx; wangxin (U) <wangxinxin.wang@xxxxxxxxxx>; > Huangweidong (C) <weidong.huang@xxxxxxxxxx>; Liujinsong (Paul) > <liu.jinsong@xxxxxxxxxx> > Subject: Re: [PATCH v3] KVM: x86: enable dirty log gradually in small chunks > > On Mon, Feb 24, 2020 at 11:25:58AM +0800, Jay Zhou wrote: > > 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@xxxxxxxxxx> > > --- > > v3: > > * add kvm_manual_dirty_log_init_set helper, add testcase on top and > > keep old behavior for KVM_MEM_READONLY [Peter] > > * tweak logic at enabling KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 > [Sean, > > Peter] > > > > v2: > > * add new bit to KVM_ENABLE_CAP for > KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 [Paolo] > > * support non-PML path [Peter] > > * delete the unnecessary ifdef and make the initialization of bitmap > > more clear [Sean] > > * document the new bits and tweak the testcase > > > > Documentation/virt/kvm/api.rst | 16 +++++++++++++--- > > arch/x86/include/asm/kvm_host.h | 3 ++- > > arch/x86/kvm/mmu/mmu.c | 7 ++++--- > > arch/x86/kvm/vmx/vmx.c | 3 ++- > > arch/x86/kvm/x86.c | 18 +++++++++++++++--- > > include/linux/kvm_host.h | 9 ++++++++- > > virt/kvm/kvm_main.c | 30 +++++++++++++++++++++++------- > > 7 files changed, 67 insertions(+), 19 deletions(-) > > > > diff --git a/Documentation/virt/kvm/api.rst > > b/Documentation/virt/kvm/api.rst index 97a72a5..807fcd7 100644 > > --- a/Documentation/virt/kvm/api.rst > > +++ b/Documentation/virt/kvm/api.rst > > @@ -5704,10 +5704,20 @@ and injected exceptions. > > :Architectures: x86, arm, arm64, mips > > :Parameters: args[0] whether feature should be enabled or not > > > > -With this capability enabled, KVM_GET_DIRTY_LOG will not > > automatically -clear and write-protect all pages that are returned as dirty. > > +Valid flags are:: > > + > > + #define KVM_DIRTY_LOG_MANUAL_PROTECT2 (1 << 0) #define > > + KVM_DIRTY_LOG_INITIALLY_SET (1 << 1) > > I think I mis-read previously on the old version so my comment was misleading. > If this is the sub-capability within KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2, > then I don't think we need to have the ending "2" any more. How about: It's OK, :-) > > KVM_MANUAL_PROTECT_ENABLE > KVM_MANUAL_PROTECT_INIT_ALL_SET I think this naming emphasizes more about "manual protect", and the original naming emphasizes more about "dirty log". The object of manual protect and initial-all-set is dirty log, so it seem that the original names are a little more close to the thing we do. > > + > > +With KVM_DIRTY_LOG_MANUAL_PROTECT2 set, KVM_GET_DIRTY_LOG will > not > > +automatically clear and write-protect all pages that are returned as dirty. > > Rather, userspace will have to do this operation separately using > > KVM_CLEAR_DIRTY_LOG. > > +With KVM_DIRTY_LOG_INITIALLY_SET set, all the bits of the dirty > > +bitmap will be initialized to 1 when created, dirty logging will be > > +enabled gradually in small chunks using KVM_CLEAR_DIRTY_LOG. > > +However, the KVM_DIRTY_LOG_INITIALLY_SET depends on > > +KVM_DIRTY_LOG_MANUAL_PROTECT2, it can not be set individually and > supports x86 only for now. > > > > At the cost of a slightly more complicated operation, this provides > > better scalability and responsiveness for two reasons. First, @@ > > -5716,7 +5726,7 @@ than requiring to sync a full memslot; this ensures > > that KVM does not take spinlocks for an extended period of time. > > Second, in some cases a large amount of time can pass between a call > > to KVM_GET_DIRTY_LOG and userspace actually using the data in the > > page. Pages can be modified -during this time, which is inefficint for both the > guest and userspace: > > +during this time, which is inefficient for both the guest and userspace: > > the guest will incur a higher penalty due to write protection faults, > > while userspace can see false reports of dirty pages. Manual > > reprotection helps reducing this time, improving guest performance > > and reducing the diff --git a/arch/x86/include/asm/kvm_host.h > > b/arch/x86/include/asm/kvm_host.h index 40a0c0f..a90630c 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > @@ -1312,7 +1312,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 > > accessed_mask, > > > > void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); void > > kvm_mmu_slot_remove_write_access(struct kvm *kvm, > > - struct kvm_memory_slot *memslot); > > + struct kvm_memory_slot *memslot, > > + int start_level); > > void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, > > const struct kvm_memory_slot *memslot); void > > kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, diff --git > > a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index > > 87e9ba2..a4e70eb 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -5860,13 +5860,14 @@ static bool slot_rmap_write_protect(struct kvm > > *kvm, } > > > > void kvm_mmu_slot_remove_write_access(struct kvm *kvm, > > - struct kvm_memory_slot *memslot) > > + struct kvm_memory_slot *memslot, > > + int start_level) > > { > > bool flush; > > > > spin_lock(&kvm->mmu_lock); > > - flush = slot_handle_all_level(kvm, memslot, slot_rmap_write_protect, > > - false); > > + flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect, > > + start_level, PT_MAX_HUGEPAGE_LEVEL, false); > > spin_unlock(&kvm->mmu_lock); > > > > /* > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index > > 3be25ec..0deb8c3 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -7201,7 +7201,8 @@ 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); > > + if (!kvm_manual_dirty_log_init_set(kvm)) > > + kvm_mmu_slot_leaf_clear_dirty(kvm, slot); > > kvm_mmu_slot_largepage_remove_write_access(kvm, slot); } > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index > > fb5d64e..f816940 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -9956,7 +9956,7 @@ static void kvm_mmu_slot_apply_flags(struct kvm > > *kvm, { > > /* Still write protect RO slot */ > > if (new->flags & KVM_MEM_READONLY) { > > - kvm_mmu_slot_remove_write_access(kvm, new); > > + kvm_mmu_slot_remove_write_access(kvm, new, > PT_PAGE_TABLE_LEVEL); > > return; > > } > > > > @@ -9993,8 +9993,20 @@ static void kvm_mmu_slot_apply_flags(struct kvm > *kvm, > > if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) { > > if (kvm_x86_ops->slot_enable_log_dirty) > > kvm_x86_ops->slot_enable_log_dirty(kvm, new); > > - else > > - kvm_mmu_slot_remove_write_access(kvm, new); > > + else { > > + int level = kvm_manual_dirty_log_init_set(kvm) ? > > + PT_DIRECTORY_LEVEL : PT_PAGE_TABLE_LEVEL; > > + > > + /* > > + * If we're with initial-all-set, we don't need > > + * to write protect any small page because > > + * they're reported as dirty already. However > > + * we still need to write-protect huge pages > > + * so that the page split can happen lazily on > > + * the first write to the huge page. > > + */ > > + kvm_mmu_slot_remove_write_access(kvm, new, level); > > + } > > } else { > > if (kvm_x86_ops->slot_disable_log_dirty) > > kvm_x86_ops->slot_disable_log_dirty(kvm, new); diff --git > > a/include/linux/kvm_host.h b/include/linux/kvm_host.h index > > e89eb67..80ada94 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -360,6 +360,13 @@ static inline unsigned long > *kvm_second_dirty_bitmap(struct kvm_memory_slot *mem > > return memslot->dirty_bitmap + len / sizeof(*memslot->dirty_bitmap); > > } > > > > +#define KVM_DIRTY_LOG_MANUAL_PROTECT2 (1 << 0) #define > > +KVM_DIRTY_LOG_INITIALLY_SET (1 << 1) #define > > +KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT2 | > \ > > + KVM_DIRTY_LOG_INITIALLY_SET) > > + > > +bool kvm_manual_dirty_log_init_set(struct kvm *kvm); > > + > > struct kvm_s390_adapter_int { > > u64 ind_addr; > > u64 summary_addr; > > @@ -493,7 +500,7 @@ struct kvm { > > #endif > > long tlbs_dirty; > > struct list_head devices; > > - bool manual_dirty_log_protect; > > + u64 manual_dirty_log_protect; > > struct dentry *debugfs_dentry; > > struct kvm_stat_data **debugfs_stat_data; > > struct srcu_struct srcu; > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index > > 70f03ce..0ffb804 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -858,11 +858,17 @@ static int kvm_vm_release(struct inode *inode, > struct file *filp) > > return 0; > > } > > > > +bool kvm_manual_dirty_log_init_set(struct kvm *kvm) { > > + return kvm->manual_dirty_log_protect & KVM_DIRTY_LOG_INITIALLY_SET; > > +} > > Nit: this can be put into kvm_host.h as inlined. I'm afraid not. I tried to do it, but it can't be compiled through. Since this function is shared between the kvm and kvm_intel(vmx part) module, it should be exported. BTW: how about using kvm_dirty_log_manual_protect and_init_set instead of kvm_manual_dirty_log_init_set (just an idea, your opinions are welcome). > > > +EXPORT_SYMBOL_GPL(kvm_manual_dirty_log_init_set); > > + > > /* > > * Allocation size is twice as large as the actual dirty bitmap size. > > * See x86's kvm_vm_ioctl_get_dirty_log() why this is needed. > > */ > > -static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot) > > +static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot) > > { > > unsigned long dirty_bytes = 2 * kvm_dirty_bitmap_bytes(memslot); > > > > @@ -1094,8 +1100,11 @@ int __kvm_set_memory_region(struct kvm *kvm, > > > > /* Allocate page dirty bitmap if needed */ > > if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) { > > - if (kvm_create_dirty_bitmap(&new) < 0) > > + if (kvm_alloc_dirty_bitmap(&new)) > > goto out_free; > > + > > + if (kvm_manual_dirty_log_init_set(kvm)) > > + bitmap_set(new.dirty_bitmap, 0, new.npages); > > } > > > > slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT); > > @@ -3310,9 +3319,6 @@ static long > kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) > > case KVM_CAP_IOEVENTFD_ANY_LENGTH: > > case KVM_CAP_CHECK_EXTENSION_VM: > > case KVM_CAP_ENABLE_CAP_VM: > > -#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT > > - case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2: > > -#endif > > return 1; > > #ifdef CONFIG_KVM_MMIO > > case KVM_CAP_COALESCED_MMIO: > > @@ -3320,6 +3326,10 @@ static long > kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) > > case KVM_CAP_COALESCED_PIO: > > return 1; > > #endif > > +#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT > > + case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2: > > + return KVM_DIRTY_LOG_MANUAL_CAPS; > > We probably can only return the new feature bit when with CONFIG_X86? How about to define different values in different architectures(see KVM_USER_MEM_SLOTS as an example), like this: diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h index c3314b2..383a8ae 100644 --- a/arch/arm/include/asm/kvm_host.h +++ b/arch/arm/include/asm/kvm_host.h @@ -23,6 +23,10 @@ #define KVM_HAVE_ONE_REG #define KVM_HALT_POLL_NS_DEFAULT 500000 +#define KVM_DIRTY_LOG_MANUAL_PROTECT (1 << 0) +#define KVM_DIRTY_LOG_INITIALLY_SET 0 +#define KVM_DIRTY_LOG_MANUAL_CAPS KVM_DIRTY_LOG_MANUAL_PROTECT + #define KVM_VCPU_MAX_FEATURES 2 #include <kvm/arm_vgic.h> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index 41204a4..503ee17 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -85,6 +85,10 @@ #define KVM_HALT_POLL_NS_DEFAULT 500000 +#define KVM_DIRTY_LOG_MANUAL_PROTECT (1 << 0) +#define KVM_DIRTY_LOG_INITIALLY_SET 0 +#define KVM_DIRTY_LOG_MANUAL_CAPS KVM_DIRTY_LOG_MANUAL_PROTECT + #ifdef CONFIG_KVM_MIPS_VZ extern unsigned long GUESTID_MASK; extern unsigned long GUESTID_FIRST_VERSION; diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 40a0c0f..ac05172 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -49,6 +49,11 @@ #define KVM_IRQCHIP_NUM_PINS KVM_IOAPIC_NUM_PINS +#define KVM_DIRTY_LOG_MANUAL_PROTECT (1 << 0) +#define KVM_DIRTY_LOG_INITIALLY_SET (1 << 1) +#define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT | \ + KVM_DIRTY_LOG_INITIALLY_SET) + /* x86-specific vcpu->requests bit members */ #define KVM_REQ_MIGRATE_TIMER KVM_ARCH_REQ(0) #define KVM_REQ_REPORT_TPR_ACCESS KVM_ARCH_REQ(1) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index e89eb67..ebd3e55 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -360,6 +360,18 @@ static inline unsigned long *kvm_second_dirty_bitmap(struct kvm_memory_slot *mem return memslot->dirty_bitmap + len / sizeof(*memslot->dirty_bitmap); } +#ifndef KVM_DIRTY_LOG_MANUAL_PROTECT +#define KVM_DIRTY_LOG_MANUAL_PROTECT 0 +#endif +#ifndef KVM_DIRTY_LOG_INITIALLY_SET +#define KVM_DIRTY_LOG_INITIALLY_SET 0 +#endif +#ifndef KVM_DIRTY_LOG_MANUAL_CAPS +#define KVM_DIRTY_LOG_MANUAL_CAPS 0 +#endif > > > +#endif > > #ifdef CONFIG_HAVE_KVM_IRQ_ROUTING > > case KVM_CAP_IRQ_ROUTING: > > return KVM_MAX_IRQ_ROUTES; > > @@ -3347,11 +3357,17 @@ static int > > kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm, { > > switch (cap->cap) { > > #ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT > > - case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2: > > - if (cap->flags || (cap->args[0] & ~1)) > > + case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2: { > > + u64 allowed_options = KVM_DIRTY_LOG_MANUAL_PROTECT2; > > + > > + if (cap->args[0] & KVM_DIRTY_LOG_MANUAL_PROTECT2) > > + allowed_options |= KVM_DIRTY_LOG_INITIALLY_SET; > > Same here to check against CONFIG_X86? Same as the above. Regards, Jay Zhou
