Re: [PATCH v10 Kernel 4/5] vfio iommu: Implementation of ioctl to for dirty pages tracking.

Yan Zhao
2019-12-17T09:59:28Z

On Tue, Dec 17, 2019 at 05:24:14PM +0800, Kirti Wankhede wrote:
>
>
> On 12/17/2019 10:45 AM, Yan Zhao wrote:
> > On Tue, Dec 17, 2019 at 04:21:39AM +0800, Kirti Wankhede wrote:
> >> VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
> >> - Start unpinned pages dirty pages tracking while migration is active and
> >> device is running, i.e. during pre-copy phase.
> >> - Stop unpinned pages dirty pages tracking. This is required to stop
> >> unpinned dirty pages tracking if migration failed or cancelled during
> >> pre-copy phase. Unpinned pages tracking is clear.
> >> - Get dirty pages bitmap. Stop unpinned dirty pages tracking and clear
> >> unpinned pages information on bitmap read. This ioctl returns bitmap of
> >> dirty pages, its user space application responsibility to copy content
> >> of dirty pages from source to destination during migration.
> >>
> >> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> >> Reviewed-by: Neo Jia <cjia@nvidia.com>
> >> ---
> >> drivers/vfio/vfio_iommu_type1.c | 210 ++++++++++++++++++++++++++++++++++++++--
> >> 1 file changed, 203 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> >> index 3f6b04f2334f..264449654d3f 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -70,6 +70,7 @@ struct vfio_iommu {
> >> unsigned int dma_avail;
> >> bool v2;
> >> bool nesting;
> >> + bool dirty_page_tracking;
> >> };
> >>
> >> struct vfio_domain {
> >> @@ -112,6 +113,7 @@ struct vfio_pfn {
> >> dma_addr_t iova; /* Device address */
> >> unsigned long pfn; /* Host pfn */
> >> atomic_t ref_count;
> >> + bool unpinned;
> >> };
> >>
> >> struct vfio_regions {
> >> @@ -244,6 +246,32 @@ static void vfio_remove_from_pfn_list(struct vfio_dma *dma,
> >> kfree(vpfn);
> >> }
> >>
> >> +static void vfio_remove_unpinned_from_pfn_list(struct vfio_dma *dma, bool warn)
> >> +{
> >> + struct rb_node *n = rb_first(&dma->pfn_list);
> >> +
> >> + for (; n; n = rb_next(n)) {
> >> + struct vfio_pfn *vpfn = rb_entry(n, struct vfio_pfn, node);
> >> +
> >> + if (warn)
> >> + WARN_ON_ONCE(vpfn->unpinned);
> >> +
> >> + if (vpfn->unpinned)
> >> + vfio_remove_from_pfn_list(dma, vpfn);
> >> + }
> >> +}
> >> +
> >> +static void vfio_remove_unpinned_from_dma_list(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);
> >> +
> >> + vfio_remove_unpinned_from_pfn_list(dma, false);
> >> + }
> >> +}
> >> +
> >> static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct vfio_dma *dma,
> >> unsigned long iova)
> >> {
> >> @@ -254,13 +282,17 @@ static struct vfio_pfn *vfio_iova_get_vfio_pfn(struct vfio_dma *dma,
> >> return vpfn;
> >> }
> >>
> >> -static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
> >> +static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn,
> >> + bool dirty_tracking)
> >> {
> >> int ret = 0;
> >>
> >> if (atomic_dec_and_test(&vpfn->ref_count)) {
> >> ret = put_pfn(vpfn->pfn, dma->prot);
> > if physical page here is put, it may cause problem when pin this iova
> > next time:
> > vfio_iommu_type1_pin_pages {
> > ...
> > vpfn = vfio_iova_get_vfio_pfn(dma, iova);
> > if (vpfn) {
> > phys_pfn[i] = vpfn->pfn;
> > continue;
> > }
> > ...
> > }
> >
>
> Good point. Fixing it as:
>
> vpfn = vfio_iova_get_vfio_pfn(dma, iova);
> if (vpfn) {
> - phys_pfn[i] = vpfn->pfn;
> - continue;
> + if (vpfn->unpinned)
> + vfio_remove_from_pfn_list(dma, vpfn);
what about updating vpfn instead?

> + else {
> + phys_pfn[i] = vpfn->pfn;
> + continue;
> + }
> }
>
>
>
> >> - vfio_remove_from_pfn_list(dma, vpfn);
> >> + if (dirty_tracking)
> >> + vpfn->unpinned = true;
> >> + else
> >> + vfio_remove_from_pfn_list(dma, vpfn);
> > so the unpinned pages before dirty page tracking is not treated as
> > dirty?
> >
>
> Yes. That's we agreed on previous version:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg663157.html
>
> >> }
> >> return ret;
> >> }
> >> @@ -504,7 +536,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, unsigned long vaddr,
> >> }
> >>
> >> static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> >> - bool do_accounting)
> >> + bool do_accounting, bool dirty_tracking)
> >> {
> >> int unlocked;
> >> struct vfio_pfn *vpfn = vfio_find_vpfn(dma, iova);
> >> @@ -512,7 +544,10 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> >> if (!vpfn)
> >> return 0;
> >>
> >> - unlocked = vfio_iova_put_vfio_pfn(dma, vpfn);
> >> + if (vpfn->unpinned)
> >> + return 0;
> >> +
> >> + unlocked = vfio_iova_put_vfio_pfn(dma, vpfn, dirty_tracking);
> >>
> >> if (do_accounting)
> >> vfio_lock_acct(dma, -unlocked, true);
> >> @@ -583,7 +618,8 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> >>
> >> ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> >> if (ret) {
> >> - vfio_unpin_page_external(dma, iova, do_accounting);
> >> + vfio_unpin_page_external(dma, iova, do_accounting,
> >> + false);
> >> goto pin_unwind;
> >> }
> >> }
> >> @@ -598,7 +634,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> >>
> >> iova = user_pfn[j] << PAGE_SHIFT;
> >> dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> >> - vfio_unpin_page_external(dma, iova, do_accounting);
> >> + vfio_unpin_page_external(dma, iova, do_accounting, false);
> >> phys_pfn[j] = 0;
> >> }
> >> pin_done:
> >> @@ -632,7 +668,8 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
> >> dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> >> if (!dma)
> >> goto unpin_exit;
> >> - vfio_unpin_page_external(dma, iova, do_accounting);
> >> + vfio_unpin_page_external(dma, iova, do_accounting,
> >> + iommu->dirty_page_tracking);
> >> }
> >>
> >> unpin_exit:
> >> @@ -850,6 +887,88 @@ static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
> >> return bitmap;
> >> }
> >>
> >> +/*
> >> + * start_iova is the reference from where bitmaping started. This is called
> >> + * from DMA_UNMAP where start_iova can be different than iova
> >> + */
> >> +
> >> +static void vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova,
> >> + size_t size, uint64_t pgsize,
> >> + dma_addr_t start_iova, unsigned long *bitmap)
> >> +{
> >> + struct vfio_dma *dma;
> >> + dma_addr_t i = iova;
> >> + unsigned long pgshift = __ffs(pgsize);
> >> +
> >> + while ((dma = vfio_find_dma(iommu, i, pgsize))) {
> >> + /* mark all pages dirty if all pages are pinned and mapped. */
> >> + if (dma->iommu_mapped) {
> > This prevents pass-through devices from calling vfio_pin_pages to do
> > fine grained log dirty.
>
> Yes, I mentioned that in yet TODO item in cover letter:
>
> "If IOMMU capable device is present in the container, then all pages are
> marked dirty. Need to think smart way to know if IOMMU capable device's
> driver is smart to report pages to be marked dirty by pinning those
> pages externally."
>
why not just check first if any vpfn present for IOMMU capable devices?

>
> >> + dma_addr_t iova_limit;
> >> +
> >> + iova_limit = (dma->iova + dma->size) < (iova + size) ?
> >> + (dma->iova + dma->size) : (iova + size);
> >> +
> >> + for (; i < iova_limit; i += pgsize) {
> >> + unsigned int start;
> >> +
> >> + start = (i - start_iova) >> pgshift;
> >> +
> >> + __bitmap_set(bitmap, start, 1);
> >> + }
> >> + if (i >= iova + size)
> >> + return;
> >> + } else {
> >> + struct rb_node *n = rb_first(&dma->pfn_list);
> >> + bool found = false;
> >> +
> >> + for (; n; n = rb_next(n)) {
> >> + struct vfio_pfn *vpfn = rb_entry(n,
> >> + struct vfio_pfn, node);
> >> + if (vpfn->iova >= i) {
> >> + found = true;
> >> + break;
> >> + }
> >> + }
> >> +
> >> + if (!found) {
> >> + i += dma->size;
> >> + continue;
> >> + }
> >> +
> >> + for (; n; n = rb_next(n)) {
> >> + unsigned int start;
> >> + struct vfio_pfn *vpfn = rb_entry(n,
> >> + struct vfio_pfn, node);
> >> +
> >> + if (vpfn->iova >= iova + size)
> >> + return;
> >> +
> >> + start = (vpfn->iova - start_iova) >> pgshift;
> >> +
> >> + __bitmap_set(bitmap, start, 1);
> >> +
> >> + i = vpfn->iova + pgsize;
> >> + }
> >> + }
> >> + vfio_remove_unpinned_from_pfn_list(dma, false);
> >> + }
> >> +}
> >> +
> >> +static long verify_bitmap_size(unsigned long npages, unsigned long bitmap_size)
> >> +{
> >> + long bsize;
> >> +
> >> + if (!bitmap_size || bitmap_size > SIZE_MAX)
> >> + return -EINVAL;
> >> +
> >> + bsize = ALIGN(npages, BITS_PER_LONG) / sizeof(unsigned long);
> >> +
> >> + if (bitmap_size < bsize)
> >> + return -EINVAL;
> >> +
> >> + return bsize;
> >> +}
> >> +
> >> static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> >> struct vfio_iommu_type1_dma_unmap *unmap)
> >> {
> >> @@ -2298,6 +2417,83 @@ 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 range;
> >> + uint32_t mask = VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
> >> + VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP |
> >> + VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP;
> >> + int ret;
> >> +
> >> + if (!iommu->v2)
> >> + return -EACCES;
> >> +
> >> + minsz = offsetofend(struct vfio_iommu_type1_dirty_bitmap,
> >> + bitmap);
> >> +
> >> + if (copy_from_user(&range, (void __user *)arg, minsz))
> >> + return -EFAULT;
> >> +
> >> + if (range.argsz < minsz || range.flags & ~mask)
> >> + return -EINVAL;
> >> +
> >> + if (range.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_START) {
> >> + iommu->dirty_page_tracking = true;
> >> + return 0;
> >> + } else if (range.flags & VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP) {
> >> + iommu->dirty_page_tracking = false;
> >> +
> >> + mutex_lock(&iommu->lock);
> >> + vfio_remove_unpinned_from_dma_list(iommu);
> >> + mutex_unlock(&iommu->lock);
> >> + return 0;
> >> +
> >> + } else if (range.flags &
> >> + VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP) {
> >> + uint64_t iommu_pgmask;
> >> + unsigned long pgshift = __ffs(range.pgsize);
> >> + unsigned long *bitmap;
> >> + long bsize;
> >> +
> >> + iommu_pgmask =
> >> + ((uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu))) - 1;
> >> +
> >> + if (((range.pgsize - 1) & iommu_pgmask) !=
> >> + (range.pgsize - 1))
> >> + return -EINVAL;
> >> +
> >> + if (range.iova & iommu_pgmask)
> >> + return -EINVAL;
> >> + if (!range.size || range.size > SIZE_MAX)
> >> + return -EINVAL;
> >> + if (range.iova + range.size < range.iova)
> >> + return -EINVAL;
> >> +
> >> + bsize = verify_bitmap_size(range.size >> pgshift,
> >> + range.bitmap_size);
> >> + if (bsize)
> >> + return ret;
> >> +
> >> + bitmap = kmalloc(bsize, GFP_KERNEL);
> >> + if (!bitmap)
> >> + return -ENOMEM;
> >> +
> >> + ret = copy_from_user(bitmap,
> >> + (void __user *)range.bitmap, bsize) ? -EFAULT : 0;
> >> + if (ret)
> >> + goto bitmap_exit;
> >> +
> >> + iommu->dirty_page_tracking = false;
> > why iommu->dirty_page_tracking is false here?
> > suppose this ioctl can be called several times.
> >
>
> This ioctl can be called several times, but once this ioctl is called
> that means vCPUs are stopped and VFIO devices are stopped (i.e. in
> stop-and-copy phase) and dirty pages bitmap are being queried by user.
>
can't agree that VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP can only be
called in stop-and-copy phase.
As stated in last version, this will cause QEMU to get a wrong expectation
of VM downtime and this is also the reason for previously pinned pages
before log_sync cannot be treated as dirty. If this get bitmap ioctl can
be called early in save_setup phase, then it's no problem even all ram
is dirty.

Thanks
Yan
>
>
> > Thanks
> > Yan
> >> + mutex_lock(&iommu->lock);
> >> + vfio_iova_dirty_bitmap(iommu, range.iova, range.size,
> >> + range.pgsize, range.iova, bitmap);
> >> + mutex_unlock(&iommu->lock);
> >> +
> >> + ret = copy_to_user((void __user *)range.bitmap, bitmap,
> >> + range.bitmap_size) ? -EFAULT : 0;
> >> +bitmap_exit:
> >> + kfree(bitmap);
> >> + return ret;
> >> + }
> >> }
> >>
> >> return -ENOTTY;
> >> --
> >> 2.7.0
> >>