[RFC][PATCH RFC 10/12] KVM: move dirty bitmaps to user space

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

We move dirty bitmaps to user space.

 - Allocation and destruction: we use do_mmap() and do_munmap().
   The new bitmap space is twice longer than the original one and we
   use the additional space for double buffering: this makes it
   possible to update the active bitmap while letting the user space
   read the other one safely. For x86, we can also remove the vmalloc()
   in kvm_vm_ioctl_get_dirty_log().

 - Bitmap manipulations: we replace all functions which access dirty
   bitmaps with *_user() functions.

 - For ia64: moving the dirty bitmaps of memory slots does not affect
   ia64 much because it's using a different place to store dirty logs
   rather than the dirty bitmaps of memory slots: all we have to change
   are sync and get of dirty log, so we don't need set_bit_user like
   functions for ia64.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
CC: Avi Kivity <avi@redhat.com>
CC: Alexander Graf <agraf@suse.de>
---
 arch/ia64/kvm/kvm-ia64.c  |   15 +++++++++-
 arch/powerpc/kvm/book3s.c |    5 +++-
 arch/x86/kvm/x86.c        |   25 ++++++++----------
 include/linux/kvm_host.h  |    3 +-
 virt/kvm/kvm_main.c       |   62 +++++++++++++++++++++++++++++++++++++-------
 5 files changed, 82 insertions(+), 28 deletions(-)

diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 17fd65c..03503e6 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1823,11 +1823,19 @@ static int kvm_ia64_sync_dirty_log(struct kvm *kvm,
 	n = kvm_dirty_bitmap_bytes(memslot);
 	base = memslot->base_gfn / BITS_PER_LONG;
 
+	r = -EFAULT;
+	if (!access_ok(VERIFY_WRITE, memslot->dirty_bitmap, n))
+		goto out;
+
 	for (i = 0; i < n/sizeof(long); ++i) {
 		if (dirty_bitmap[base + i])
 			memslot->is_dirty = true;
 
-		memslot->dirty_bitmap[i] = dirty_bitmap[base + i];
+		if (__put_user(dirty_bitmap[base + i],
+			       &memslot->dirty_bitmap[i])) {
+			r = -EFAULT;
+			goto out;
+		}
 		dirty_bitmap[base + i] = 0;
 	}
 	r = 0;
@@ -1858,7 +1866,10 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 	if (memslot->is_dirty) {
 		kvm_flush_remote_tlbs(kvm);
 		n = kvm_dirty_bitmap_bytes(memslot);
-		memset(memslot->dirty_bitmap, 0, n);
+		if (clear_user(memslot->dirty_bitmap, n)) {
+			r = -EFAULT;
+			goto out;
+		}
 		memslot->is_dirty = false;
 	}
 	r = 0;
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 4b074f1..2a31d2f 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -1210,7 +1210,10 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 			kvmppc_mmu_pte_pflush(vcpu, ga, ga_end);
 
 		n = kvm_dirty_bitmap_bytes(memslot);
-		memset(memslot->dirty_bitmap, 0, n);
+		if (clear_user(memslot->dirty_bitmap, n)) {
+			r = -EFAULT;
+			goto out;
+		}
 		memslot->is_dirty = false;
 	}
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 023c7f8..32a3d94 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2760,40 +2760,37 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 	/* If nothing is dirty, don't bother messing with page tables. */
 	if (memslot->is_dirty) {
 		struct kvm_memslots *slots, *old_slots;
-		unsigned long *dirty_bitmap;
+		unsigned long __user *dirty_bitmap;
+		unsigned long __user *dirty_bitmap_old;
 
 		spin_lock(&kvm->mmu_lock);
 		kvm_mmu_slot_remove_write_access(kvm, log->slot);
 		spin_unlock(&kvm->mmu_lock);
 
-		r = -ENOMEM;
-		dirty_bitmap = vmalloc(n);
-		if (!dirty_bitmap)
+		dirty_bitmap = memslot->dirty_bitmap;
+		dirty_bitmap_old = memslot->dirty_bitmap_old;
+		r = -EFAULT;
+		if (clear_user(dirty_bitmap_old, n))
 			goto out;
-		memset(dirty_bitmap, 0, n);
 
 		r = -ENOMEM;
 		slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
-		if (!slots) {
-			vfree(dirty_bitmap);
+		if (!slots)
 			goto out;
-		}
+
 		memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
-		slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
+		slots->memslots[log->slot].dirty_bitmap = dirty_bitmap_old;
+		slots->memslots[log->slot].dirty_bitmap_old = dirty_bitmap;
 		slots->memslots[log->slot].is_dirty = false;
 
 		old_slots = kvm->memslots;
 		rcu_assign_pointer(kvm->memslots, slots);
 		synchronize_srcu_expedited(&kvm->srcu);
-		dirty_bitmap = old_slots->memslots[log->slot].dirty_bitmap;
 		kfree(old_slots);
 
 		r = -EFAULT;
-		if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) {
-			vfree(dirty_bitmap);
+		if (copy_in_user(log->dirty_bitmap, dirty_bitmap, n))
 			goto out;
-		}
-		vfree(dirty_bitmap);
 	} else {
 		r = -EFAULT;
 		if (clear_user(log->dirty_bitmap, n))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0aa6ecb..c95e2b7 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -116,7 +116,8 @@ struct kvm_memory_slot {
 	unsigned long npages;
 	unsigned long flags;
 	unsigned long *rmap;
-	unsigned long *dirty_bitmap;
+	unsigned long __user *dirty_bitmap;
+	unsigned long __user *dirty_bitmap_old;
 	bool is_dirty;
 	struct {
 		unsigned long rmap_pde;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3e3acad..ddcf65a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -437,8 +437,20 @@ out_err_nodisable:
 
 static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
 {
-	vfree(memslot->dirty_bitmap);
+	unsigned long user_addr;
+	unsigned long n = kvm_dirty_bitmap_bytes(memslot);
+
+	if (!memslot->dirty_bitmap)
+		return;
+
+	user_addr = min((unsigned long)memslot->dirty_bitmap,
+			(unsigned long)memslot->dirty_bitmap_old);
+	down_write(&current->mm->mmap_sem);
+	do_munmap(current->mm, user_addr, 2 * n);
+	up_write(&current->mm->mmap_sem);
+
 	memslot->dirty_bitmap = NULL;
+	memslot->dirty_bitmap_old = NULL;
 }
 
 /*
@@ -472,8 +484,12 @@ void kvm_free_physmem(struct kvm *kvm)
 	int i;
 	struct kvm_memslots *slots = kvm->memslots;
 
-	for (i = 0; i < slots->nmemslots; ++i)
+	for (i = 0; i < slots->nmemslots; ++i) {
+		/* VM process will exit: we don't unmap by ourselves. */
+		slots->memslots[i].dirty_bitmap = NULL;
+		slots->memslots[i].dirty_bitmap_old = NULL;
 		kvm_free_physmem_slot(&slots->memslots[i], NULL);
+	}
 
 	kfree(kvm->memslots);
 }
@@ -527,14 +543,35 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
 
 static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
 {
-	unsigned long dirty_bytes = kvm_dirty_bitmap_bytes(memslot);
+	int err;
+	unsigned long user_addr;
+	unsigned long n = kvm_dirty_bitmap_bytes(memslot);
 
-	memslot->dirty_bitmap = vmalloc(dirty_bytes);
-	if (!memslot->dirty_bitmap)
-		return -ENOMEM;
+	down_write(&current->mm->mmap_sem);
+	user_addr = do_mmap(NULL, 0, 2 * n,
+			    PROT_READ | PROT_WRITE,
+			    MAP_PRIVATE | MAP_ANONYMOUS, 0);
+	up_write(&current->mm->mmap_sem);
+
+	if (IS_ERR((void *)user_addr)) {
+		err = PTR_ERR((void *)user_addr);
+		goto out;
+	}
+
+	memslot->dirty_bitmap = (unsigned long __user *)user_addr;
+	memslot->dirty_bitmap_old = (unsigned long __user *)(user_addr + n);
+	if (clear_user(memslot->dirty_bitmap, 2 * n)) {
+		err = -EFAULT;
+		goto out_unmap;
+	}
 
-	memset(memslot->dirty_bitmap, 0, dirty_bytes);
 	return 0;
+out_unmap:
+	down_write(&current->mm->mmap_sem);
+	do_munmap(current->mm, user_addr, 2 * n);
+	up_write(&current->mm->mmap_sem);
+out:
+	return err;
 }
 
 /*
@@ -799,7 +836,7 @@ int kvm_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
 	n = kvm_dirty_bitmap_bytes(memslot);
 
 	r = -EFAULT;
-	if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
+	if (copy_in_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
 		goto out;
 
 	r = 0;
@@ -1195,11 +1232,16 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
 	gfn = unalias_gfn(kvm, gfn);
 	memslot = gfn_to_memslot_unaliased(kvm, gfn);
 	if (memslot && memslot->dirty_bitmap) {
-		unsigned long rel_gfn = gfn - memslot->base_gfn;
+		int nr = generic_le_bit_offset(gfn - memslot->base_gfn);
 
-		generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
+		if (kvm_set_bit_user(nr, memslot->dirty_bitmap))
+			goto out_fault;
 		memslot->is_dirty = true;
 	}
+	return;
+
+out_fault:
+	printk(KERN_WARNING "%s: kvm_set_bit_user failed.\n", __func__);
 }
 
 /*
-- 
1.7.0.4