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


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