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

[Yan Zhao]

On Fri, Mar 20, 2020 at 12:57:30AM +0800, Kirti Wankhede wrote:
> 
> 
> On 3/19/2020 6:36 PM, Alex Williamson wrote:
> > On Thu, 19 Mar 2020 02:15:34 -0400
> > Yan Zhao <address@hidden> wrote:
> > 
> >> On Thu, Mar 19, 2020 at 12:40:53PM +0800, Alex Williamson wrote:
> >>> On Thu, 19 Mar 2020 00:15:33 -0400
> >>> Yan Zhao <address@hidden> wrote:
> >>>    
> >>>> On Thu, Mar 19, 2020 at 12:01:00PM +0800, Alex Williamson wrote:
> >>>>> On Wed, 18 Mar 2020 23:06:39 -0400
> >>>>> Yan Zhao <address@hidden> wrote:
> >>>>>      
> >>>>>> On Thu, Mar 19, 2020 at 03:41:11AM +0800, Kirti Wankhede 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 <address@hidden>
> >>>>>>> Reviewed-by: Neo Jia <address@hidden>
> >>>>>>> ---
> >>>>>>>   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;
> >>>>>>>   };
> >>>>>>>   
> >>>>>>>   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)
> >>>>>>> +{
> >>>>>>> +     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;
> >>>>>>> +
> >>>>>> looks this size is passed from user. how can it ensure size always
> >>>>>> equals to dma->size ?
> >>>>>>
> >>>>>> shouldn't we iterate dma tree to look for dirty for whole range if a
> >>>>>> single dma cannot meet them all?
> >>>>>
> >>>>> Please see the discussion on v12[1], the problem is with the alignment
> >>>>> of DMA mapped regions versus the bitmap.  A DMA mapping only requires
> >>>>> page alignment, so for example imagine a user requests the bitmap from
> >>>>> page zero to 4GB, but we have a DMA mapping starting at 4KB.  We can't
> >>>>> efficiently copy the bitmap tracked by the vfio_dma structure to the
> >>>>> user buffer when it's shifted by 1 bit.  Adjacent mappings can also
> >>>>> make for a very complicated implementation.  In the discussion linked
> >>>>> we decided to compromise on a more simple implementation that requires
> >>>>> the user to ask for a bitmap which exactly matches a single DMA
> >>>>> mapping, which Kirti indicates is what we require to support QEMU.
> >>>>> Later in the series, the unmap operation also makes this requirement
> >>>>> when used with the flags to retrieve the dirty bitmap.  Thanks,
> >>>>>     
> >>>>
> >>>> so, what about for vIOMMU enabling case?
> >>>> if IOVAs are mapped per page, then there's a log_sync in qemu,
> >>>> it's supposed for range from 0-U64MAX, qemu has to find out which
> >>>> ones are mapped and cut them into pages before calling this IOCTL?
> >>>> And what if those IOVAs are mapped for len more than one page?
> >>>
> >>> Good question.  Kirti?
> >>>
> 
> In log_sync with vIOMMU, loop for range such that:
> 
> - find iotlb entry for iova, get iova_xlat
> - size = iotlb.addr_mask + 1; This is same caculation as when mapping 
> are created from vfio_iommu_map_notify()
> - use the <iova_xlat, size> for VFIO_IOMMU_DIRTY_PAGES ioctl
> - increment iova: iova += size
> - iterate above steps till end of range.
>
Ok. It makes sense, though not efficient :)
think about when there's no iotlb found for an iova, page by page
incremental of iova is required. right?

> >>>>> [1] https://lore.kernel.org/kvm/address@hidden/
> >>>>>       
> >>>>>>> +     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;
> >>>>>>> +
> >> Here, dma->bitmap needs to be cleared. right?
> > 
> > Ah, I missed re-checking this in my review.  v13 did clear it, but I
> > noted that we need to re-populate any currently pinned pages.  This
> > neither clears nor repopulates.  That's wrong.  Thanks,
> > 
> 
> Why re-populate when there will be no change since 
> vfio_iova_dirty_bitmap() is called holding iommu->lock? If there is any 
> pin request while vfio_iova_dirty_bitmap() is still working, it will 
> wait till iommu->lock is released. Bitmap will be populated when page is 
> pinned.
> 
> Thanks,
> Kirti
> 
> > Alex
> >   
> >>>>>>> +     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)
> >>>>>>> +             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)
> >>>>>>>   {
> >>>>>>> @@ -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
> >>>>>>>               *copied = __copy_from_user(data, (void __user *)vaddr,
> >>>>>>>                                          count) ? 0 : count;
> >>>>>>>       if (kthread)
> >>>>>>> -- 
> >>>>>>> 2.7.0
> >>>>>>>        
> >>>>>>      
> >>>>>      
> >>>>    
> >>>    
> >>
> >