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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Yan Zhao (yan.y.zhao@intel.com) wrote:
> On Tue, Dec 17, 2019 at 07:47:05PM +0800, Kirti Wankhede wrote:
> > 
> > 
> > On 12/17/2019 3:21 PM, Yan Zhao wrote:
> > > 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?
> > > 
> > 
> > vfio_pin_page_external() takes care of verification checks and mem lock 
> > accounting. I prefer to free existing and add new node with existing 
> > functions.
> > 
> > >> +                       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?
> > > 
> > 
> > vfio_pin_pages(dev, ...) calls driver->ops->pin_pages(iommu, ...)
> > 
> > In vfio_iommu_type1 module, vfio_iommu_type1_pin_pages() doesn't know 
> > the device. vpfn are tracked against container->iommu, not against 
> > device. Need to think of smart way to know if devices in container are 
> > all smart which report pages dirty ny pinning those pages manually.
> >
> I believe in such case, the mdev on top of device is in the same iommu
> group (i.e. 1:1 mdev on top of device).
> device vendor driver calls vfio_pin_pages to notify vfio which pages are dirty. 
> > 
> > >>
> > >>>> +			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.
> > > 
> > 
> > Device can also write to pages which are pinned, and then there is no 
> > way to know pages dirtied by device during pre-copy phase.
> > If user ask dirty bitmap in per-copy phase, even then user will have to 
> > query dirty bitmap in stop-and-copy phase where this will be superset 
> > including all pages reported during pre-copy. Then instead of copying 
> > all pages twice, its better to do it once during stop-and-copy phase.
> >
> I think the flow should be like this:
> 1. save_setup --> GET_BITMAP ioctl --> return bitmap for currently + previously
> pinned pages and clean all previously pinned pages
> 
> 2. save_pending --> GET_BITMAP ioctl  --> return bitmap of (currently
> pinned pages + previously pinned pages since last clean) and clean all
> previously pinned pages
> 
> 3. save_complete_precopy --> GET_BITMAP ioctl --> return bitmap of (currently
> pinned pages + previously pinned pages since last clean) and clean all
> previously pinned pages
> 
> 
> Copying pinned pages multiple times is unavoidable because those pinned pages
> are always treated as dirty. That's per vendor's implementation.
> But if the pinned pages are not reported as dirty before stop-and-copy phase,
> QEMU would think dirty pages has converged
> and enter blackout phase, making downtime_limit severely incorrect.

I'm not sure it's any worse.
I *think* we do a last sync after we've decided to go to stop-and-copy;
wont that then mark all those pages as dirty again, so it'll have the
same behaviour?
Anyway, it seems wrong to repeatedly send pages that you know are
pointless - but that probably means we need a way to mark those somehow
to avoid it.

Dave

> 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
> > >>>>
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK