1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * KVM dirty ring implementation 4 * 5 * Copyright 2019 Red Hat, Inc. 6 */ 7 #include <linux/kvm_host.h> 8 #include <linux/kvm.h> 9 #include <linux/vmalloc.h> 10 #include <linux/kvm_dirty_ring.h> 11 #include <trace/events/kvm.h> 12 #include "kvm_mm.h" 13 14 int __weak kvm_cpu_dirty_log_size(void) 15 { 16 return 0; 17 } 18 19 u32 kvm_dirty_ring_get_rsvd_entries(void) 20 { 21 return KVM_DIRTY_RING_RSVD_ENTRIES + kvm_cpu_dirty_log_size(); 22 } 23 24 bool kvm_use_dirty_bitmap(struct kvm *kvm) 25 { 26 lockdep_assert_held(&kvm->slots_lock); 27 28 return !kvm->dirty_ring_size || kvm->dirty_ring_with_bitmap; 29 } 30 31 #ifndef CONFIG_NEED_KVM_DIRTY_RING_WITH_BITMAP 32 bool kvm_arch_allow_write_without_running_vcpu(struct kvm *kvm) 33 { 34 return false; 35 } 36 #endif 37 38 static u32 kvm_dirty_ring_used(struct kvm_dirty_ring *ring) 39 { 40 return READ_ONCE(ring->dirty_index) - READ_ONCE(ring->reset_index); 41 } 42 43 static bool kvm_dirty_ring_soft_full(struct kvm_dirty_ring *ring) 44 { 45 return kvm_dirty_ring_used(ring) >= ring->soft_limit; 46 } 47 48 static bool kvm_dirty_ring_full(struct kvm_dirty_ring *ring) 49 { 50 return kvm_dirty_ring_used(ring) >= ring->size; 51 } 52 53 static void kvm_reset_dirty_gfn(struct kvm *kvm, u32 slot, u64 offset, u64 mask) 54 { 55 struct kvm_memory_slot *memslot; 56 int as_id, id; 57 58 if (!mask) 59 return; 60 61 as_id = slot >> 16; 62 id = (u16)slot; 63 64 if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_USER_MEM_SLOTS) 65 return; 66 67 memslot = id_to_memslot(__kvm_memslots(kvm, as_id), id); 68 69 if (!memslot || (offset + __fls(mask)) >= memslot->npages) 70 return; 71 72 KVM_MMU_LOCK(kvm); 73 kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, offset, mask); 74 KVM_MMU_UNLOCK(kvm); 75 } 76 77 int kvm_dirty_ring_alloc(struct kvm_dirty_ring *ring, int index, u32 size) 78 { 79 ring->dirty_gfns = vzalloc(size); 80 if (!ring->dirty_gfns) 81 return -ENOMEM; 82 83 ring->size = size / sizeof(struct kvm_dirty_gfn); 84 ring->soft_limit = ring->size - kvm_dirty_ring_get_rsvd_entries(); 85 ring->dirty_index = 0; 86 ring->reset_index = 0; 87 ring->index = index; 88 89 return 0; 90 } 91 92 static inline void kvm_dirty_gfn_set_invalid(struct kvm_dirty_gfn *gfn) 93 { 94 smp_store_release(&gfn->flags, 0); 95 } 96 97 static inline void kvm_dirty_gfn_set_dirtied(struct kvm_dirty_gfn *gfn) 98 { 99 gfn->flags = KVM_DIRTY_GFN_F_DIRTY; 100 } 101 102 static inline bool kvm_dirty_gfn_harvested(struct kvm_dirty_gfn *gfn) 103 { 104 return smp_load_acquire(&gfn->flags) & KVM_DIRTY_GFN_F_RESET; 105 } 106 107 int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring) 108 { 109 u32 cur_slot, next_slot; 110 u64 cur_offset, next_offset; 111 unsigned long mask; 112 int count = 0; 113 struct kvm_dirty_gfn *entry; 114 bool first_round = true; 115 116 /* This is only needed to make compilers happy */ 117 cur_slot = cur_offset = mask = 0; 118 119 while (true) { 120 entry = &ring->dirty_gfns[ring->reset_index & (ring->size - 1)]; 121 122 if (!kvm_dirty_gfn_harvested(entry)) 123 break; 124 125 next_slot = READ_ONCE(entry->slot); 126 next_offset = READ_ONCE(entry->offset); 127 128 /* Update the flags to reflect that this GFN is reset */ 129 kvm_dirty_gfn_set_invalid(entry); 130 131 ring->reset_index++; 132 count++; 133 /* 134 * Try to coalesce the reset operations when the guest is 135 * scanning pages in the same slot. 136 */ 137 if (!first_round && next_slot == cur_slot) { 138 s64 delta = next_offset - cur_offset; 139 140 if (delta >= 0 && delta < BITS_PER_LONG) { 141 mask |= 1ull << delta; 142 continue; 143 } 144 145 /* Backwards visit, careful about overflows! */ 146 if (delta > -BITS_PER_LONG && delta < 0 && 147 (mask << -delta >> -delta) == mask) { 148 cur_offset = next_offset; 149 mask = (mask << -delta) | 1; 150 continue; 151 } 152 } 153 kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask); 154 cur_slot = next_slot; 155 cur_offset = next_offset; 156 mask = 1; 157 first_round = false; 158 } 159 160 kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask); 161 162 /* 163 * The request KVM_REQ_DIRTY_RING_SOFT_FULL will be cleared 164 * by the VCPU thread next time when it enters the guest. 165 */ 166 167 trace_kvm_dirty_ring_reset(ring); 168 169 return count; 170 } 171 172 void kvm_dirty_ring_push(struct kvm_vcpu *vcpu, u32 slot, u64 offset) 173 { 174 struct kvm_dirty_ring *ring = &vcpu->dirty_ring; 175 struct kvm_dirty_gfn *entry; 176 177 /* It should never get full */ 178 WARN_ON_ONCE(kvm_dirty_ring_full(ring)); 179 180 entry = &ring->dirty_gfns[ring->dirty_index & (ring->size - 1)]; 181 182 entry->slot = slot; 183 entry->offset = offset; 184 /* 185 * Make sure the data is filled in before we publish this to 186 * the userspace program. There's no paired kernel-side reader. 187 */ 188 smp_wmb(); 189 kvm_dirty_gfn_set_dirtied(entry); 190 ring->dirty_index++; 191 trace_kvm_dirty_ring_push(ring, slot, offset); 192 193 if (kvm_dirty_ring_soft_full(ring)) 194 kvm_make_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu); 195 } 196 197 bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu) 198 { 199 /* 200 * The VCPU isn't runnable when the dirty ring becomes soft full. 201 * The KVM_REQ_DIRTY_RING_SOFT_FULL event is always set to prevent 202 * the VCPU from running until the dirty pages are harvested and 203 * the dirty ring is reset by userspace. 204 */ 205 if (kvm_check_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu) && 206 kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) { 207 kvm_make_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu); 208 vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL; 209 trace_kvm_dirty_ring_exit(vcpu); 210 return true; 211 } 212 213 return false; 214 } 215 216 struct page *kvm_dirty_ring_get_page(struct kvm_dirty_ring *ring, u32 offset) 217 { 218 return vmalloc_to_page((void *)ring->dirty_gfns + offset * PAGE_SIZE); 219 } 220 221 void kvm_dirty_ring_free(struct kvm_dirty_ring *ring) 222 { 223 vfree(ring->dirty_gfns); 224 ring->dirty_gfns = NULL; 225 } 226