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| From: | Kirti Wankhede |
| Subject: | Re: [PATCH Kernel v20 6/8] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap |
| Date: | Fri, 15 May 2020 21:00:32 +0530 |
| User-agent: | Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 |
On 5/15/2020 7:01 PM, Alex Williamson wrote:
On Fri, 15 May 2020 12:17:03 +0530 Kirti Wankhede <address@hidden> wrote:On 5/15/2020 11:17 AM, Alex Williamson wrote:On Fri, 15 May 2020 09:46:43 +0530 Kirti Wankhede <address@hidden> wrote:On 5/15/2020 8:57 AM, Alex Williamson wrote:On Fri, 15 May 2020 02:07:45 +0530 Kirti Wankhede <address@hidden> wrote:DMA mapped pages, including those pinned by mdev vendor drivers, might get unpinned and unmapped while migration is active and device is still running. For example, in pre-copy phase while guest driver could access those pages, host device or vendor driver can dirty these mapped pages. Such pages should be marked dirty so as to maintain memory consistency for a user making use of dirty page tracking. To get bitmap during unmap, user should allocate memory for bitmap, set it all zeros, set size of allocated memory, set page size to be considered for bitmap and set flag VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP. Signed-off-by: Kirti Wankhede <address@hidden> Reviewed-by: Neo Jia <address@hidden> --- drivers/vfio/vfio_iommu_type1.c | 77 ++++++++++++++++++++++++++++++++++------- include/uapi/linux/vfio.h | 10 ++++++ 2 files changed, 75 insertions(+), 12 deletions(-) diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index b76d3b14abfd..a1dc57bcece5 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -195,11 +195,15 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old) static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, size_t pgsize) { uint64_t npages = dma->size / pgsize; + size_t bitmap_size;if (npages > DIRTY_BITMAP_PAGES_MAX)return -EINVAL;- dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);+ /* Allocate extra 64 bits which are used for bitmap manipulation */ + bitmap_size = DIRTY_BITMAP_BYTES(npages) + sizeof(u64); + + dma->bitmap = kvzalloc(bitmap_size, GFP_KERNEL); if (!dma->bitmap) return -ENOMEM;@@ -999,23 +1003,25 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)}static int vfio_dma_do_unmap(struct vfio_iommu *iommu,- struct vfio_iommu_type1_dma_unmap *unmap) + struct vfio_iommu_type1_dma_unmap *unmap, + struct vfio_bitmap *bitmap) { - uint64_t mask; struct vfio_dma *dma, *dma_last = NULL; - size_t unmapped = 0; + size_t unmapped = 0, pgsize; int ret = 0, retries = 0; + unsigned long pgshift;mutex_lock(&iommu->lock); - mask = ((uint64_t)1 << __ffs(iommu->pgsize_bitmap)) - 1;+ pgshift = __ffs(iommu->pgsize_bitmap); + pgsize = (size_t)1 << pgshift;- if (unmap->iova & mask) {+ if (unmap->iova & (pgsize - 1)) { ret = -EINVAL; goto unlock; }- if (!unmap->size || unmap->size & mask) {+ if (!unmap->size || unmap->size & (pgsize - 1)) { ret = -EINVAL; goto unlock; } @@ -1026,9 +1032,15 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, goto unlock; }- WARN_ON(mask & PAGE_MASK);-again: + /* When dirty tracking is enabled, allow only min supported pgsize */ + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) && + (!iommu->dirty_page_tracking || (bitmap->pgsize != pgsize))) { + ret = -EINVAL; + goto unlock; + }+ WARN_ON((pgsize - 1) & PAGE_MASK);+again: /* * vfio-iommu-type1 (v1) - User mappings were coalesced together to * avoid tracking individual mappings. This means that the granularity @@ -1066,6 +1078,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, ret = -EINVAL; goto unlock; } + dma = vfio_find_dma(iommu, unmap->iova + unmap->size - 1, 0); if (dma && dma->iova + dma->size != unmap->iova + unmap->size) { ret = -EINVAL; @@ -1083,6 +1096,23 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, if (dma->task->mm != current->mm) break;+ if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&+ (dma_last != dma)) { + + /* + * mark all pages dirty if all pages are pinned and + * mapped + */ + if (dma->iommu_mapped) + bitmap_set(dma->bitmap, 0, + dma->size >> pgshift);Nit, all the callers of update_user_bitmap() precede the call with this identical operation, we should probably push it into the function to do it.+ + ret = update_user_bitmap(bitmap->data, dma, + unmap->iova, pgsize); + if (ret) + break; + } +As noted last time, the above is just busy work if pfn_list is not already empty. The entire code block above should be moved to after the block below. Thanks,pfn_list will be empty for IOMMU backed devices where all pages are pinned and mapped,Unless we're making use of the selective dirtying introduced in patch 8/8 or the container is shared with non-IOMMU backed mdevs.but those should be reported as dirty.I'm confused how that justifies or requires this ordering.1. non IOMMU mdev device: - vendor driver pins pages - pfn_list is not empty - device dma or write to pinned pages 2. IOMMU backed mdev device or vfio device, but smart driver which pins required pages - vendor driver pins pages - pfn_list is not empty - device dma or write to pinned pages 3. IOMMU backed mdev device or vfio device, driver is not smart - pages are pinned and mapped during attach - pfn_list is empty - device dma or write to any of pinned pages For case 3, here this function does bitmap_set(dma->bitmap), that is mark all pages dirty and then accordingly copy bitmap to user buffer. Copying dma->bitmap logic remains same.What dependency does case 3 have on pfn_list? Why does it matter if that bitmap_set() occurs before or after we've drained pfn_list? How do we know we're in case 3 before we've looked at pfn_list?
If update_user_bitmap() is moved in if block like:
if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
update_user_bitmap()
...
}
then update_user_bitmap() would never get called for case 3.
So moved it back above empty pfn_list check.Sorry, it still doesn't make any sense to me, and with no discussion I can't differentiate ignored comments from discarded comments. Pages in the pfn_list contribute to the dirty bitmap when they're pinned, we don't depend on pfn_list when reporting the dirty bitmap except for re-populating pfn_list dirtied pages after the bitmap has been cleared. We're unmapping the dma, so that's not the case here. Also since update_user_bitmap() shifts the bitmap in place now, any repetitive calls will give us incorrect results.Right, but this is unmapping and freeing vfio_dmaTherefore, as I see it, we _can_ take the branch below and when we do any work we've done above is not only wasted but may lead to incorrect data copied to the user if we shift dma->bitmap in place more than once. Please explain in more detail if you believe this is still correct. Thanks,In this case also bitmap copy to user happens once, (dma_last != dma) takes care of making sure that its called only once.I did miss the dma_last check, so that prevents us from repeating this path, BUT we release iommu->lock if we enter the pfn_list !empty path. The moment we do that, we might unblock a vendor driver trying to pin or rw more pages. So the bitmap we've copied to the user might be stale and incorrect. I don't see why this is so contentious, what is the actual disadvantage to moving this until after we've drained pfn_list? The risks seem abundant to me. Thanks,
Sorry if I misinterpreted earlier, are you proposing to move update_user_bitmap() after this if block?
if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
...
}
I thought you are asking to move it in block.
That makes sense. I'll update the patch in send next version in some time.
Thanks,
Kirti
Alexif (!RB_EMPTY_ROOT(&dma->pfn_list)) { struct vfio_iommu_type1_dma_unmap nb_unmap;@@ -2447,17 +2477,40 @@ static long vfio_iommu_type1_ioctl(void *iommu_data, } else if (cmd == VFIO_IOMMU_UNMAP_DMA) {struct vfio_iommu_type1_dma_unmap unmap; - long ret; + struct vfio_bitmap bitmap = { 0 }; + int ret;minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size); if (copy_from_user(&unmap, (void __user *)arg, minsz))return -EFAULT;- if (unmap.argsz < minsz || unmap.flags)+ if (unmap.argsz < minsz || + unmap.flags & ~VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) return -EINVAL;- ret = vfio_dma_do_unmap(iommu, &unmap);+ if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) { + unsigned long pgshift; + + if (unmap.argsz < (minsz + sizeof(bitmap))) + return -EINVAL; + + if (copy_from_user(&bitmap, + (void __user *)(arg + minsz), + sizeof(bitmap))) + return -EFAULT; + + if (!access_ok((void __user *)bitmap.data, bitmap.size)) + return -EINVAL; + + pgshift = __ffs(bitmap.pgsize); + ret = verify_bitmap_size(unmap.size >> pgshift, + bitmap.size); + if (ret) + return ret; + } + + ret = vfio_dma_do_unmap(iommu, &unmap, &bitmap); if (ret) return ret;diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.hindex 123de3bc2dce..0a0c7315ddd6 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -1048,12 +1048,22 @@ struct vfio_bitmap { * field. No guarantee is made to the user that arbitrary unmaps of iova * or size different from those used in the original mapping call will * succeed. + * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP should be set to get dirty bitmap + * before unmapping IO virtual addresses. When this flag is set, user must + * provide data[] as structure vfio_bitmap. User must allocate memory to get + * bitmap, zero the bitmap memory and must set size of allocated memory in + * vfio_bitmap.size field. A bit in bitmap represents one page of user provided + * page size in 'pgsize', consecutively starting from iova offset. Bit set + * indicates page at that offset from iova is dirty. Bitmap of pages in the + * range of unmapped size is returned in vfio_bitmap.data */ struct vfio_iommu_type1_dma_unmap { __u32 argsz; __u32 flags; +#define VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP (1 << 0) __u64 iova; /* IO virtual address */ __u64 size; /* Size of mapping (bytes) */ + __u8 data[]; };#define VFIO_IOMMU_UNMAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 14)
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