> -----Original Message----- > From: kvm-owner@xxxxxxxxxxxxxxx <kvm-owner@xxxxxxxxxxxxxxx> On Behalf > Of Alex Williamson > Sent: Tuesday, March 31, 2020 10:38 AM > To: Zhao, Yan Y <yan.y.zhao@xxxxxxxxx> > Cc: Kirti Wankhede <kwankhede@xxxxxxxxxx>; cjia@xxxxxxxxxx; Tian, Kevin > <kevin.tian@xxxxxxxxx>; Yang, Ziye <ziye.yang@xxxxxxxxx>; Liu, Changpeng > <changpeng.liu@xxxxxxxxx>; Liu, Yi L <yi.l.liu@xxxxxxxxx>; > mlevitsk@xxxxxxxxxx; eskultet@xxxxxxxxxx; cohuck@xxxxxxxxxx; > dgilbert@xxxxxxxxxx; jonathan.davies@xxxxxxxxxxx; eauger@xxxxxxxxxx; > aik@xxxxxxxxx; pasic@xxxxxxxxxxxxx; felipe@xxxxxxxxxxx; > Zhengxiao.zx@xxxxxxxxxxxxxxx; shuangtai.tst@xxxxxxxxxxxxxxx; > Ken.Xue@xxxxxxx; Wang, Zhi A <zhi.a.wang@xxxxxxxxx>; qemu- > devel@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > Subject: Re: [PATCH v16 Kernel 4/7] vfio iommu: Implementation of ioctl for > dirty pages tracking. > > On Mon, 30 Mar 2020 21:16:21 -0400 > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > On Tue, Mar 31, 2020 at 09:12:59AM +0800, Alex Williamson wrote: > > > On Mon, 30 Mar 2020 20:50:47 -0400 > > > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > > > > > On Tue, Mar 31, 2020 at 08:53:47AM +0800, Alex Williamson wrote: > > > > > 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, > > > > > > > > if we always uses PAGE_SIZE, why not use PAGE_SIZE directly? > > > > or returning dirty bitmap unit (e.g. 1 << > > > > __ffs(vfio_pgsize_bitmap(iommu))) to QEMU in > > > > VFIO_IOMMU_DIRTY_PAGES_FLAG_START, so that qemu can do > possible conversion if it's not the same unit that QEMU uses. > > > > > > The vfio interface is essentially just an extension of the IOMMU API > > > via domain->pgsize_bitmap. intel-iommu mostly made the bitmask > > > meaningless by reporting essentially PAGE_MASK, and we just expose > > > the common version of that across potentially all the IOMMUs used by > > > the domain, modulo minimum of PAGE_SIZE. Thanks, > > > > ok. got it. do you think it's good to return this iommu page size when > > turning on dirty page tracking? so when GET_BITMAP ioctl comes, we > > don't need to quit if range.bitmap.pgsize != iommu_pgsize. > > instead, the GET_BITMAP can success with iommu page size and qemu > does > > the bitmap conversion afterwards. > > The bitmap is already expose to the user via > vfio_iommu_type1_info.iova_pgsizes in the VFIO_IOMMU_GET_INFO ioctl. > Our original intention was to allow the user to specify the dirty bitmap page > size, which is still enabled in the ioctl via bitmap.pgsize, but for simplification > we currently only support the smallest page size. This could be something > else we expose via the extension interface when more page sizes are > supported. Thanks, > Ok. Got it . Thanks
