Re: [PATCH v14 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking.

Kirti Wankhede
2020-03-19T14:52:57Z

On 3/19/2020 9:15 AM, Alex Williamson wrote:
> On Thu, 19 Mar 2020 01:11:11 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
>> VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
>> - Start dirty pages tracking while migration is active
>> - Stop dirty pages tracking.
>> - Get dirty pages bitmap. Its user space application's responsibility to
>> copy content of dirty pages from source to destination during migration.
>>
>> To prevent DoS attack, memory for bitmap is allocated per vfio_dma
>> structure. Bitmap size is calculated considering smallest supported page
>> size. Bitmap is allocated for all vfio_dmas when dirty logging is enabled
>>
>> Bitmap is populated for already pinned pages when bitmap is allocated for
>> a vfio_dma with the smallest supported page size. Update bitmap from
>> pinning functions when tracking is enabled. When user application queries
>> bitmap, check if requested page size is same as page size used to
>> populated bitmap. If it is equal, copy bitmap, but if not equal, return
>> error.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 205 +++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 203 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 70aeab921d0f..d6417fb02174 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -71,6 +71,7 @@ struct vfio_iommu {
>> unsigned int dma_avail;
>> bool v2;
>> bool nesting;
>> + bool dirty_page_tracking;
>> };
>>
>> struct vfio_domain {
>> @@ -91,6 +92,7 @@ struct vfio_dma {
>> bool lock_cap; /* capable(CAP_IPC_LOCK) */
>> struct task_struct *task;
>> struct rb_root pfn_list; /* Ex-user pinned pfn list */
>> + unsigned long *bitmap;
>
> We've made the bitmap a width invariant u64 else, should be here as
> well.
>
>> };
>>
>> struct vfio_group {
>> @@ -125,7 +127,10 @@ struct vfio_regions {
>> #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) \
>> (!list_empty(&iommu->domain_list))
>>
>> +#define DIRTY_BITMAP_BYTES(n) (ALIGN(n, BITS_PER_TYPE(u64)) / BITS_PER_BYTE)
>> +
>> static int put_pfn(unsigned long pfn, int prot);
>> +static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu);
>>
>> /*
>> * This code handles mapping and unmapping of user data buffers
>> @@ -175,6 +180,55 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old)
>> rb_erase(&old->node, &iommu->dma_list);
>> }
>>
>> +static int vfio_dma_bitmap_alloc(struct vfio_iommu *iommu, uint64_t pgsize)
>> +{
>> + struct rb_node *n = rb_first(&iommu->dma_list);
>> +
>> + for (; n; n = rb_next(n)) {
>> + struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
>> + struct rb_node *p;
>> + unsigned long npages = dma->size / pgsize;
>> +
>> + dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
>> + if (!dma->bitmap) {
>> + struct rb_node *p = rb_prev(n);
>> +
>> + for (; p; p = rb_prev(p)) {
>> + struct vfio_dma *dma = rb_entry(n,
>> + struct vfio_dma, node);
>> +
>> + kfree(dma->bitmap);
>> + dma->bitmap = NULL;
>> + }
>> + return -ENOMEM;
>> + }
>> +
>> + if (RB_EMPTY_ROOT(&dma->pfn_list))
>> + continue;
>> +
>> + for (p = rb_first(&dma->pfn_list); p; p = rb_next(p)) {
>> + struct vfio_pfn *vpfn = rb_entry(p, struct vfio_pfn,
>> + node);
>> +
>> + bitmap_set(dma->bitmap,
>> + (vpfn->iova - dma->iova) / pgsize, 1);
>> + }
>> + }
>> + return 0;
>> +}
>> +
>> +static void vfio_dma_bitmap_free(struct vfio_iommu *iommu)
>> +{
>> + struct rb_node *n = rb_first(&iommu->dma_list);
>> +
>> + for (; n; n = rb_next(n)) {
>> + struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
>> +
>> + kfree(dma->bitmap);
>> + dma->bitmap = NULL;
>> + }
>> +}
>> +
>> /*
>> * Helper Functions for host iova-pfn list
>> */
>> @@ -567,6 +621,14 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>> vfio_unpin_page_external(dma, iova, do_accounting);
>> goto pin_unwind;
>> }
>> +
>> + if (iommu->dirty_page_tracking) {
>> + unsigned long pgshift =
>> + __ffs(vfio_pgsize_bitmap(iommu));
>> +
>> + bitmap_set(dma->bitmap,
>> + (vpfn->iova - dma->iova) >> pgshift, 1);
>> + }
>> }
>>
>> ret = i;
>> @@ -801,6 +863,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>> vfio_unmap_unpin(iommu, dma, true);
>> vfio_unlink_dma(iommu, dma);
>> put_task_struct(dma->task);
>> + kfree(dma->bitmap);
>> kfree(dma);
>> iommu->dma_avail++;
>> }
>> @@ -831,6 +894,50 @@ static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
>> return bitmap;
>> }
>>
>> +static int vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova,
>> + size_t size, uint64_t pgsize,
>> + unsigned char __user *bitmap)
>
> And here, why do callers cast to an unsigned char pointer when we're
> going to cast to a void pointer anyway? Should be a u64 __user pointer.
>
>> +{
>> + struct vfio_dma *dma;
>> + unsigned long pgshift = __ffs(pgsize);
>> + unsigned int npages, bitmap_size;
>> +
>> + dma = vfio_find_dma(iommu, iova, 1);
>> +
>> + if (!dma)
>> + return -EINVAL;
>> +
>> + if (dma->iova != iova || dma->size != size)
>> + return -EINVAL;
>> +
>> + npages = dma->size >> pgshift;
>> + bitmap_size = DIRTY_BITMAP_BYTES(npages);
>> +
>> + /* mark all pages dirty if all pages are pinned and mapped. */
>> + if (dma->iommu_mapped)
>> + bitmap_set(dma->bitmap, 0, npages);
>> +
>> + if (copy_to_user((void __user *)bitmap, dma->bitmap, bitmap_size))
>> + return -EFAULT;
>> +
>> + return 0;
>> +}
>> +
>> +static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
>> +{
>> + uint64_t bsize;
>> +
>> + if (!npages || !bitmap_size || bitmap_size > UINT_MAX)
>
> As commented previously, how do we derive this UINT_MAX limitation?
>

Sorry, I missed that earlier

> UINT_MAX seems arbitrary, is this specified in our API? The size of a
> vfio_dma is limited to what the user is able to pin, and therefore
> their locked memory limit, but do we have an explicit limit elsewhere
> that results in this limit here. I think a 4GB bitmap would track
> something like 2^47 bytes of memory, that's pretty excessive, but still
> an arbitrary limit.

There has to be some upper limit check. In core KVM, in
virt/kvm/kvm_main.c there is max number of pages check:

if (new.npages > KVM_MEM_MAX_NR_PAGES)

Where
/*
* Some of the bitops functions do not support too long bitmaps.
* This number must be determined not to exceed such limits.
*/
#define KVM_MEM_MAX_NR_PAGES ((1UL << 31) - 1)

Though I don't know which bitops functions do not support long bitmaps.

Something similar as above can be done or same as you also mentioned of
4GB bitmap limit? that is U32_MAX instead of UINT_MAX?

>> + return -EINVAL;
>> +
>> + bsize = DIRTY_BITMAP_BYTES(npages);
>> +
>> + if (bitmap_size < bsize)
>> + return -EINVAL;
>> +
>> + return 0;
>> +}
>> +
>> static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> struct vfio_iommu_type1_dma_unmap *unmap)
>> {
>
> We didn't address that vfio_dma_do_map() needs to kvzalloc a bitmap for
> any new vfio_dma created while iommu->dirty_page_tracking = true.
>

Good point. Adding it.

Thanks,
Kirti

>> @@ -2278,6 +2385,93 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>
>> return copy_to_user((void __user *)arg, &unmap, minsz) ?
>> -EFAULT : 0;
>> + } else if (cmd == VFIO_IOMMU_DIRTY_PAGES) {
>> + struct vfio_iommu_type1_dirty_bitmap dirty;
>> + uint32_t mask = VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
>> + VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP |
>> + VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP;
>> + int ret = 0;
>> +
>> + if (!iommu->v2)
>> + return -EACCES;
>> +
>> + minsz = offsetofend(struct vfio_iommu_type1_dirty_bitmap,
>> + flags);
>> +
>> + if (copy_from_user(&dirty, (void __user *)arg, minsz))
>> + return -EFAULT;
>> +
>> + if (dirty.argsz < minsz || dirty.flags & ~mask)
>> + return -EINVAL;
>> +
>> + /* only one flag should be set at a time */
>> + if (__ffs(dirty.flags) != __fls(dirty.flags))
>> + return -EINVAL;
>> +
>> + if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_START) {
>> + uint64_t pgsize = 1 << __ffs(vfio_pgsize_bitmap(iommu));
>> +
>> + mutex_lock(&iommu->lock);
>> + if (!iommu->dirty_page_tracking) {
>> + ret = vfio_dma_bitmap_alloc(iommu, pgsize);
>> + if (!ret)
>> + iommu->dirty_page_tracking = true;
>> + }
>> + mutex_unlock(&iommu->lock);
>> + return ret;
>> + } else if (dirty.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP) {
>> + mutex_lock(&iommu->lock);
>> + if (iommu->dirty_page_tracking) {
>> + iommu->dirty_page_tracking = false;
>> + vfio_dma_bitmap_free(iommu);
>> + }
>> + mutex_unlock(&iommu->lock);
>> + return 0;
>> + } else if (dirty.flags &
>> + VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP) {
>> + struct vfio_iommu_type1_dirty_bitmap_get range;
>> + unsigned long pgshift;
>> + size_t data_size = dirty.argsz - minsz;
>> + uint64_t iommu_pgsize =
>> + 1 << __ffs(vfio_pgsize_bitmap(iommu));
>> +
>> + if (!data_size || data_size < sizeof(range))
>> + return -EINVAL;
>> +
>> + if (copy_from_user(&range, (void __user *)(arg + minsz),
>> + sizeof(range)))
>> + return -EFAULT;
>> +
>> + /* allow only min supported pgsize */
>> + if (range.bitmap.pgsize != iommu_pgsize)
>> + return -EINVAL;
>> + if (range.iova & (iommu_pgsize - 1))
>> + return -EINVAL;
>> + if (!range.size || range.size & (iommu_pgsize - 1))
>> + return -EINVAL;
>> + if (range.iova + range.size < range.iova)
>> + return -EINVAL;
>> + if (!access_ok((void __user *)range.bitmap.data,
>> + range.bitmap.size))
>> + return -EINVAL;
>> +
>> + pgshift = __ffs(range.bitmap.pgsize);
>> + ret = verify_bitmap_size(range.size >> pgshift,
>> + range.bitmap.size);
>> + if (ret)
>> + return ret;
>> +
>> + mutex_lock(&iommu->lock);
>> + if (iommu->dirty_page_tracking)
>> + ret = vfio_iova_dirty_bitmap(iommu, range.iova,
>> + range.size, range.bitmap.pgsize,
>> + (unsigned char __user *)range.bitmap.data);
>> + else
>> + ret = -EINVAL;
>> + mutex_unlock(&iommu->lock);
>> +
>> + return ret;
>> + }
>> }
>>
>> return -ENOTTY;
>> @@ -2345,10 +2539,17 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
>>
>> vaddr = dma->vaddr + offset;
>>
>> - if (write)
>> + if (write) {
>> *copied = __copy_to_user((void __user *)vaddr, data,
>> count) ? 0 : count;
>> - else
>> + if (*copied && iommu->dirty_page_tracking) {
>> + unsigned long pgshift =
>> + __ffs(vfio_pgsize_bitmap(iommu));
>> +
>> + bitmap_set(dma->bitmap, offset >> pgshift,
>> + *copied >> pgshift);
>> + }
>> + } else
>
> Great, thanks for adding this!
>
>> *copied = __copy_from_user(data, (void __user *)vaddr,
>> count) ? 0 : count;
>> if (kthread)
>