Re: [PATCH RFC 03/19] iommufd: Dirty tracking data support

Joao Martins
2022-05-02T12:07:29Z

On 4/30/22 05:11, Baolu Lu wrote:
> On 2022/4/29 05:09, Joao Martins wrote:
>> Add an IO pagetable API iopt_read_and_clear_dirty_data() that
>> performs the reading of dirty IOPTEs for a given IOVA range and
>> then copying back to userspace from each area-internal bitmap.
>>
>> Underneath it uses the IOMMU equivalent API which will read the
>> dirty bits, as well as atomically clearing the IOPTE dirty bit
>> and flushing the IOTLB at the end. The dirty bitmaps pass an
>> iotlb_gather to allow batching the dirty-bit updates.
>>
>> Most of the complexity, though, is in the handling of the user
>> bitmaps to avoid copies back and forth. The bitmap user addresses
>> need to be iterated through, pinned and then passing the pages
>> into iommu core. The amount of bitmap data passed at a time for a
>> read_and_clear_dirty() is 1 page worth of pinned base page
>> pointers. That equates to 16M bits, or rather 64G of data that
>> can be returned as 'dirtied'. The flush the IOTLB at the end of
>> the whole scanned IOVA range, to defer as much as possible the
>> potential DMA performance penalty.
>>
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>> ---
>> drivers/iommu/iommufd/io_pagetable.c | 169 ++++++++++++++++++++++++
>> drivers/iommu/iommufd/iommufd_private.h | 44 ++++++
>> 2 files changed, 213 insertions(+)
>>
>> diff --git a/drivers/iommu/iommufd/io_pagetable.c b/drivers/iommu/iommufd/io_pagetable.c
>> index f4609ef369e0..835b5040fce9 100644
>> --- a/drivers/iommu/iommufd/io_pagetable.c
>> +++ b/drivers/iommu/iommufd/io_pagetable.c
>> @@ -14,6 +14,7 @@
>> #include <linux/err.h>
>> #include <linux/slab.h>
>> #include <linux/errno.h>
>> +#include <uapi/linux/iommufd.h>
>>
>> #include "io_pagetable.h"
>>
>> @@ -347,6 +348,174 @@ int iopt_set_dirty_tracking(struct io_pagetable *iopt,
>> return ret;
>> }
>>
>> +int iommufd_dirty_iter_init(struct iommufd_dirty_iter *iter,
>> + struct iommufd_dirty_data *bitmap)
>> +{
>> + struct iommu_dirty_bitmap *dirty = &iter->dirty;
>> + unsigned long bitmap_len;
>> +
>> + bitmap_len = dirty_bitmap_bytes(bitmap->length >> dirty->pgshift);
>> +
>> + import_single_range(WRITE, bitmap->data, bitmap_len,
>> + &iter->bitmap_iov, &iter->bitmap_iter);
>> + iter->iova = bitmap->iova;
>> +
>> + /* Can record up to 64G at a time */
>> + dirty->pages = (struct page **) __get_free_page(GFP_KERNEL);
>> +
>> + return !dirty->pages ? -ENOMEM : 0;
>> +}
>> +
>> +void iommufd_dirty_iter_free(struct iommufd_dirty_iter *iter)
>> +{
>> + struct iommu_dirty_bitmap *dirty = &iter->dirty;
>> +
>> + if (dirty->pages) {
>> + free_page((unsigned long) dirty->pages);
>> + dirty->pages = NULL;
>> + }
>> +}
>> +
>> +bool iommufd_dirty_iter_done(struct iommufd_dirty_iter *iter)
>> +{
>> + return iov_iter_count(&iter->bitmap_iter) > 0;
>> +}
>> +
>> +static inline unsigned long iommufd_dirty_iter_bytes(struct iommufd_dirty_iter *iter)
>> +{
>> + unsigned long left = iter->bitmap_iter.count - iter->bitmap_iter.iov_offset;
>> +
>> + left = min_t(unsigned long, left, (iter->dirty.npages << PAGE_SHIFT));
>> +
>> + return left;
>> +}
>> +
>> +unsigned long iommufd_dirty_iova_length(struct iommufd_dirty_iter *iter)
>> +{
>> + unsigned long left = iommufd_dirty_iter_bytes(iter);
>> +
>> + return ((BITS_PER_BYTE * left) << iter->dirty.pgshift);
>> +}
>> +
>> +unsigned long iommufd_dirty_iova(struct iommufd_dirty_iter *iter)
>> +{
>> + unsigned long skip = iter->bitmap_iter.iov_offset;
>> +
>> + return iter->iova + ((BITS_PER_BYTE * skip) << iter->dirty.pgshift);
>> +}
>> +
>> +void iommufd_dirty_iter_advance(struct iommufd_dirty_iter *iter)
>> +{
>> + iov_iter_advance(&iter->bitmap_iter, iommufd_dirty_iter_bytes(iter));
>> +}
>> +
>> +void iommufd_dirty_iter_put(struct iommufd_dirty_iter *iter)
>> +{
>> + struct iommu_dirty_bitmap *dirty = &iter->dirty;
>> +
>> + if (dirty->npages)
>> + unpin_user_pages(dirty->pages, dirty->npages);
>> +}
>> +
>> +int iommufd_dirty_iter_get(struct iommufd_dirty_iter *iter)
>> +{
>> + struct iommu_dirty_bitmap *dirty = &iter->dirty;
>> + unsigned long npages;
>> + unsigned long ret;
>> + void *addr;
>> +
>> + addr = iter->bitmap_iov.iov_base + iter->bitmap_iter.iov_offset;
>> + npages = iov_iter_npages(&iter->bitmap_iter,
>> + PAGE_SIZE / sizeof(struct page *));
>> +
>> + ret = pin_user_pages_fast((unsigned long) addr, npages,
>> + FOLL_WRITE, dirty->pages);
>> + if (ret <= 0)
>> + return -EINVAL;
>> +
>> + dirty->npages = ret;
>> + dirty->iova = iommufd_dirty_iova(iter);
>> + dirty->start_offset = offset_in_page(addr);
>> + return 0;
>> +}
>> +
>> +static int iommu_read_and_clear_dirty(struct iommu_domain *domain,
>> + struct iommufd_dirty_data *bitmap)
>
> This looks more like a helper in the iommu core. How about
>
> iommufd_read_clear_domain_dirty()?
>
Heh, I guess that's more accurate naming indeed. I can switch to that.

>> +{
>> + const struct iommu_domain_ops *ops = domain->ops;
>> + struct iommu_iotlb_gather gather;
>> + struct iommufd_dirty_iter iter;
>> + int ret = 0;
>> +
>> + if (!ops || !ops->read_and_clear_dirty)
>> + return -EOPNOTSUPP;
>> +
>> + iommu_dirty_bitmap_init(&iter.dirty, bitmap->iova,
>> + __ffs(bitmap->page_size), &gather);
>> + ret = iommufd_dirty_iter_init(&iter, bitmap);
>> + if (ret)
>> + return -ENOMEM;
>> +
>> + for (; iommufd_dirty_iter_done(&iter);
>> + iommufd_dirty_iter_advance(&iter)) {
>> + ret = iommufd_dirty_iter_get(&iter);
>> + if (ret)
>> + break;
>> +
>> + ret = ops->read_and_clear_dirty(domain,
>> + iommufd_dirty_iova(&iter),
>> + iommufd_dirty_iova_length(&iter), &iter.dirty);
>> +
>> + iommufd_dirty_iter_put(&iter);
>> +
>> + if (ret)
>> + break;
>> + }
>> +
>> + iommu_iotlb_sync(domain, &gather);
>> + iommufd_dirty_iter_free(&iter);
>> +
>> + return ret;
>> +}
>> +
>> +int iopt_read_and_clear_dirty_data(struct io_pagetable *iopt,
>> + struct iommu_domain *domain,
>> + struct iommufd_dirty_data *bitmap)
>> +{
>> + unsigned long iova, length, iova_end;
>> + struct iommu_domain *dom;
>> + struct iopt_area *area;
>> + unsigned long index;
>> + int ret = -EOPNOTSUPP;
>> +
>> + iova = bitmap->iova;
>> + length = bitmap->length - 1;
>> + if (check_add_overflow(iova, length, &iova_end))
>> + return -EOVERFLOW;
>> +
>> + down_read(&iopt->iova_rwsem);
>> + area = iopt_find_exact_area(iopt, iova, iova_end);
>> + if (!area) {
>> + up_read(&iopt->iova_rwsem);
>> + return -ENOENT;
>> + }
>> +
>> + if (!domain) {
>> + down_read(&iopt->domains_rwsem);
>> + xa_for_each(&iopt->domains, index, dom) {
>> + ret = iommu_read_and_clear_dirty(dom, bitmap);
>
> Perhaps use @domain directly, hence no need the @dom?
>
> xa_for_each(&iopt->domains, index, domain) {
> ret = iommu_read_and_clear_dirty(domain, bitmap);
>
Yeap.

>> + if (ret)
>> + break;
>> + }
>> + up_read(&iopt->domains_rwsem);
>> + } else {
>> + ret = iommu_read_and_clear_dirty(domain, bitmap);
>> + }
>> +
>> + up_read(&iopt->iova_rwsem);
>> + return ret;
>> +}
>> +
>> struct iopt_pages *iopt_get_pages(struct io_pagetable *iopt, unsigned long iova,
>> unsigned long *start_byte,
>> unsigned long length)
>> diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
>> index d00ef3b785c5..4c12b4a8f1a6 100644
>> --- a/drivers/iommu/iommufd/iommufd_private.h
>> +++ b/drivers/iommu/iommufd/iommufd_private.h
>> @@ -8,6 +8,8 @@
>> #include <linux/xarray.h>
>> #include <linux/refcount.h>
>> #include <linux/uaccess.h>
>> +#include <linux/iommu.h>
>> +#include <linux/uio.h>
>>
>> struct iommu_domain;
>> struct iommu_group;
>> @@ -49,8 +51,50 @@ int iopt_unmap_iova(struct io_pagetable *iopt, unsigned long iova,
>> unsigned long length);
>> int iopt_unmap_all(struct io_pagetable *iopt);
>>
>> +struct iommufd_dirty_data {
>> + unsigned long iova;
>> + unsigned long length;
>> + unsigned long page_size;
>> + unsigned long *data;
>> +};
>
> How about adding some comments around this struct? Any alingment
> requirement for iova/length? What does the @data stand for?
>
I'll add them.

Albeit this structure eventually gets moved to iommu-core later in
the series when we add the UAPI and it has some comments documenting it.

I don't cover the the alignment though, but it's the same restrictions
as IOAS map/unmap (iopt_alignment essentially) which is the smaller-page-size
supported by IOMMU hw.

>> +
>> int iopt_set_dirty_tracking(struct io_pagetable *iopt,
>> struct iommu_domain *domain, bool enable);
>> +int iopt_read_and_clear_dirty_data(struct io_pagetable *iopt,
>> + struct iommu_domain *domain,
>> + struct iommufd_dirty_data *bitmap);
>> +
>> +struct iommufd_dirty_iter {
>> + struct iommu_dirty_bitmap dirty;
>> + struct iovec bitmap_iov;
>> + struct iov_iter bitmap_iter;
>> + unsigned long iova;
>> +};
>
> Same here.
>
Yes, this one deserves some comments.

Most of it is state for gup/pup and iterating the bitmap user addresses
to make iommu_dirty_bitmap_record() work only with kva.

>> +
>> +void iommufd_dirty_iter_put(struct iommufd_dirty_iter *iter);
>> +int iommufd_dirty_iter_get(struct iommufd_dirty_iter *iter);
>> +int iommufd_dirty_iter_init(struct iommufd_dirty_iter *iter,
>> + struct iommufd_dirty_data *bitmap);
>> +void iommufd_dirty_iter_free(struct iommufd_dirty_iter *iter);
>> +bool iommufd_dirty_iter_done(struct iommufd_dirty_iter *iter);
>> +void iommufd_dirty_iter_advance(struct iommufd_dirty_iter *iter);
>> +unsigned long iommufd_dirty_iova_length(struct iommufd_dirty_iter *iter);
>> +unsigned long iommufd_dirty_iova(struct iommufd_dirty_iter *iter);
>> +static inline unsigned long dirty_bitmap_bytes(unsigned long nr_pages)
>> +{
>> + return (ALIGN(nr_pages, BITS_PER_TYPE(u64)) / BITS_PER_BYTE);
>> +}
>> +
>> +/*
>> + * Input argument of number of bits to bitmap_set() is unsigned integer, which
>> + * further casts to signed integer for unaligned multi-bit operation,
>> + * __bitmap_set().
>> + * Then maximum bitmap size supported is 2^31 bits divided by 2^3 bits/byte,
>> + * that is 2^28 (256 MB) which maps to 2^31 * 2^12 = 2^43 (8TB) on 4K page
>> + * system.
>> + */
>> +#define DIRTY_BITMAP_PAGES_MAX ((u64)INT_MAX)
>> +#define DIRTY_BITMAP_SIZE_MAX dirty_bitmap_bytes(DIRTY_BITMAP_PAGES_MAX)
>>
>> int iopt_access_pages(struct io_pagetable *iopt, unsigned long iova,
>> unsigned long npages, struct page **out_pages, bool write);
>
> Best regards,
> baolu