diff options
| -rw-r--r-- | arch/x86/kvm/x86.c | 116 |
1 files changed, 43 insertions, 73 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 813ebf1..0d9a578 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3067,55 +3067,32 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm, } /** - * write_protect_slot - write protect a slot for dirty logging - * @kvm: the kvm instance - * @memslot: the slot we protect - * @dirty_bitmap: the bitmap indicating which pages are dirty - * @nr_dirty_pages: the number of dirty pages + * kvm_vm_ioctl_get_dirty_log - get and clear the log of dirty pages in a slot + * @kvm: kvm instance + * @log: slot id and address to which we copy the log * - * We have two ways to find all sptes to protect: - * 1. Use kvm_mmu_slot_remove_write_access() which walks all shadow pages and - * checks ones that have a spte mapping a page in the slot. - * 2. Use kvm_mmu_rmap_write_protect() for each gfn found in the bitmap. + * We need to keep it in mind that VCPU threads can write to the bitmap + * concurrently. So, to avoid losing data, we keep the following order for + * each bit: * - * Generally speaking, if there are not so many dirty pages compared to the - * number of shadow pages, we should use the latter. + * 1. Take a snapshot of the bit and clear it if needed. + * 2. Write protect the corresponding page. + * 3. Flush TLB's if needed. + * 4. Copy the snapshot to the userspace. * - * Note that letting others write into a page marked dirty in the old bitmap - * by using the remaining tlb entry is not a problem. That page will become - * write protected again when we flush the tlb and then be reported dirty to - * the user space by copying the old bitmap. + * Between 2 and 3, the guest may write to the page using the remaining TLB + * entry. This is not a problem because the page will be reported dirty at + * step 4 using the snapshot taken before and step 3 ensures that successive + * writes will be logged for the next call. */ -static void write_protect_slot(struct kvm *kvm, - struct kvm_memory_slot *memslot, - unsigned long *dirty_bitmap, - unsigned long nr_dirty_pages) -{ - spin_lock(&kvm->mmu_lock); - - /* Not many dirty pages compared to # of shadow pages. */ - if (nr_dirty_pages < kvm->arch.n_used_mmu_pages) { - gfn_t offset; - - for_each_set_bit(offset, dirty_bitmap, memslot->npages) - kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, 1); - - kvm_flush_remote_tlbs(kvm); - } else - kvm_mmu_slot_remove_write_access(kvm, memslot->id); - - spin_unlock(&kvm->mmu_lock); -} - -/* - * Get (and clear) the dirty memory log for a memory slot. - */ -int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, - struct kvm_dirty_log *log) +int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log) { int r; struct kvm_memory_slot *memslot; - unsigned long n, nr_dirty_pages; + unsigned long n, i; + unsigned long *dirty_bitmap; + unsigned long *dirty_bitmap_buffer; + bool is_dirty = false; mutex_lock(&kvm->slots_lock); @@ -3124,49 +3101,42 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, goto out; memslot = id_to_memslot(kvm->memslots, log->slot); + + dirty_bitmap = memslot->dirty_bitmap; r = -ENOENT; - if (!memslot->dirty_bitmap) + if (!dirty_bitmap) goto out; n = kvm_dirty_bitmap_bytes(memslot); - nr_dirty_pages = memslot->nr_dirty_pages; - /* If nothing is dirty, don't bother messing with page tables. */ - if (nr_dirty_pages) { - struct kvm_memslots *slots, *old_slots; - unsigned long *dirty_bitmap, *dirty_bitmap_head; + dirty_bitmap_buffer = dirty_bitmap + n / sizeof(long); + memset(dirty_bitmap_buffer, 0, n); - dirty_bitmap = memslot->dirty_bitmap; - dirty_bitmap_head = memslot->dirty_bitmap_head; - if (dirty_bitmap == dirty_bitmap_head) - dirty_bitmap_head += n / sizeof(long); - memset(dirty_bitmap_head, 0, n); + spin_lock(&kvm->mmu_lock); - r = -ENOMEM; - slots = kmemdup(kvm->memslots, sizeof(*kvm->memslots), GFP_KERNEL); - if (!slots) - goto out; + for (i = 0; i < n / sizeof(long); i++) { + unsigned long mask; + gfn_t offset; - memslot = id_to_memslot(slots, log->slot); - memslot->nr_dirty_pages = 0; - memslot->dirty_bitmap = dirty_bitmap_head; - update_memslots(slots, NULL); + if (!dirty_bitmap[i]) + continue; - old_slots = kvm->memslots; - rcu_assign_pointer(kvm->memslots, slots); - synchronize_srcu_expedited(&kvm->srcu); - kfree(old_slots); + is_dirty = true; - write_protect_slot(kvm, memslot, dirty_bitmap, nr_dirty_pages); + mask = xchg(&dirty_bitmap[i], 0); + dirty_bitmap_buffer[i] = mask; - r = -EFAULT; - if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) - goto out; - } else { - r = -EFAULT; - if (clear_user(log->dirty_bitmap, n)) - goto out; + offset = i * BITS_PER_LONG; + kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, mask); } + if (is_dirty) + kvm_flush_remote_tlbs(kvm); + + spin_unlock(&kvm->mmu_lock); + + r = -EFAULT; + if (copy_to_user(log->dirty_bitmap, dirty_bitmap_buffer, n)) + goto out; r = 0; out: |