On Mon, 30 Mar 2020 19:51:31 -0400 Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > On Mon, Mar 30, 2020 at 09:49:21PM +0800, Kirti Wankhede wrote: > > > > > > On 3/30/2020 8:54 AM, Yan Zhao wrote: > > > On Fri, Mar 27, 2020 at 01:28:13PM +0800, Kirti Wankhede wrote: > > >> Hit send button little early. > > >> > > >> > > > >> > I checked v12, it's not like what I said. > > >> > In v12, bitmaps are generated per vfio_dma, and combination of the > > >> > bitmaps are required in order to generate a big bitmap suiting for dirty > > >> > query. It can cause problem when offset not aligning. > > >> > But what I propose here is to generate an rb tree orthogonal to the tree > > >> > of vfio_dma. > > >> > > > >> > as to CPU cycles saving, I don't think iterating/translating page by page > > >> > would achieve that purpose. > > >> > > > >> > > >> Instead of creating one extra rb tree for dirty pages tracking in v10 > > >> tried to use dma->pfn_list itself, we tried changes in v10, v11 and v12, > > >> latest version is evolved version with best possible approach after > > >> discussion. Probably, go through v11 as well. > > >> https://patchwork.kernel.org/patch/11298335/ > > >> > > > I'm not sure why all those previous implementations are bound to > > > vfio_dma. for vIOMMU on, in most cases, a vfio_dma is only for a page, > > > so generating a one-byte bitmap for a single page in each vfio_dma ? > > > is it possible to creating one extra rb tree to keep dirty ranges, and > > > one fixed length kernel bitmap whose content is generated on query, > > > serving as a bouncing buffer for copy_to_user > > > > > > > One fixed length? what should be fixed value? then isn't it better to > > fix the size to dma->size? > > > > This is also to prevent DoS attack, user space application can query a > > very large range. > > > > >> > > >> On 3/27/2020 6:00 AM, Yan Zhao wrote: > > >>> On Fri, Mar 27, 2020 at 05:39:01AM +0800, Kirti Wankhede wrote: > > >>>> > > >>>> > > >>>> On 3/25/2020 7:41 AM, Yan Zhao wrote: > > >>>>> On Wed, Mar 25, 2020 at 05:18:52AM +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 <kwankhede@xxxxxxxxxx> > > >>>>>> Reviewed-by: Neo Jia <cjia@xxxxxxxxxx> > > >>>>>> --- > > >>>>>> drivers/vfio/vfio_iommu_type1.c | 266 +++++++++++++++++++++++++++++++++++++++- > > >>>>>> 1 file changed, 260 insertions(+), 6 deletions(-) > > >>>>>> > > >>>>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > > >>>>>> index 70aeab921d0f..874a1a7ae925 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 +127,21 @@ 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) > > >>>>>> + > > >>>>>> +/* > > >>>>>> + * 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 (uint64_t)(INT_MAX - 1) > > >>>>>> +#define DIRTY_BITMAP_SIZE_MAX DIRTY_BITMAP_BYTES(DIRTY_BITMAP_PAGES_MAX) > > >>>>>> + > > >>>>>> 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 +191,77 @@ 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_dma *dma, uint64_t pgsize) > > >>>>>> +{ > > >>>>>> + uint64_t npages = dma->size / pgsize; > > >>>>>> + > > > If pgsize > dma->size, npages = 0. > > > wouldn't it cause problem? > > > > > > > This patch-set supports bitmap for smallest supported page size, i.e. > > PAGE_SIZE. vfio_dma_do_map() validates dma->size accordingly. So this > > case will not happen. > > > as far as I know, qemu/kvm uses 4k as the unit for dirty page tracking. > so why smallest iommu page size is used here? > wouldn't it cause problem? If your concern is that the IOMMU supports sub-4K page sizes, see vfio_pgsize_bitmap(). We actually only support PAGE_SIZE as our minimum mapping unit, even if the IOMMU supports less, so PAGE_SIZE is our lower bound. Thanks, Alex
