Re: [PATCH v26 13/17] vfio: create mapped iova list when vIOMMU is enabled

[Kirti Wankhede]

On 10/19/2020 10:54 PM, Alex Williamson wrote:
> On Mon, 19 Oct 2020 11:31:03 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
> > On 9/26/2020 3:53 AM, Alex Williamson wrote:
> > > On Wed, 23 Sep 2020 04:54:15 +0530
> > > Kirti Wankhede <kwankhede@nvidia.com> wrote:
> > >    
> > > > Create mapped iova list when vIOMMU is enabled. For each mapped iova
> > > > save translated address. Add node to list on MAP and remove node from
> > > > list on UNMAP.
> > > > This list is used to track dirty pages during migration.
> > > >
> > > > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > > > ---
> > > >    hw/vfio/common.c              | 58 
> > > > ++++++++++++++++++++++++++++++++++++++-----
> > > >    include/hw/vfio/vfio-common.h |  8 ++++++
> > > >    2 files changed, 60 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > > > index d4959c036dd1..dc56cded2d95 100644
> > > > --- a/hw/vfio/common.c
> > > > +++ b/hw/vfio/common.c
> > > > @@ -407,8 +407,8 @@ static bool 
> > > > vfio_listener_skipped_section(MemoryRegionSection *section)
> > > >    }
> > > >    
> > > >    /* Called with rcu_read_lock held.  */
> > > > -static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, void **vaddr,
> > > > -                           bool *read_only)
> > > > +static bool vfio_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> > > > +                               ram_addr_t *ram_addr, bool *read_only)
> > > >    {
> > > >        MemoryRegion *mr;
> > > >        hwaddr xlat;
> > > > @@ -439,8 +439,17 @@ static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, void 
> > > > **vaddr,
> > > >            return false;
> > > >        }
> > > >    
> > > > -    *vaddr = memory_region_get_ram_ptr(mr) + xlat;
> > > > -    *read_only = !writable || mr->readonly;
> > > > +    if (vaddr) {
> > > > +        *vaddr = memory_region_get_ram_ptr(mr) + xlat;
> > > > +    }
> > > > +
> > > > +    if (ram_addr) {
> > > > +        *ram_addr = memory_region_get_ram_addr(mr) + xlat;
> > > > +    }
> > > > +
> > > > +    if (read_only) {
> > > > +        *read_only = !writable || mr->readonly;
> > > > +    }
> > > >    
> > > >        return true;
> > > >    }
> > > > @@ -450,7 +459,6 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, 
> > > > IOMMUTLBEntry *iotlb)
> > > >        VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
> > > >        VFIOContainer *container = giommu->container;
> > > >        hwaddr iova = iotlb->iova + giommu->iommu_offset;
> > > > -    bool read_only;
> > > >        void *vaddr;
> > > >        int ret;
> > > >    
> > > > @@ -466,7 +474,10 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> > > >        rcu_read_lock();
> > > >    
> > > >        if ((iotlb->perm & IOMMU_RW) != IOMMU_NONE) {
> > > > -        if (!vfio_get_vaddr(iotlb, &vaddr, &read_only)) {
> > > > +        ram_addr_t ram_addr;
> > > > +        bool read_only;
> > > > +
> > > > +        if (!vfio_get_xlat_addr(iotlb, &vaddr, &ram_addr, &read_only)) {
> > > >                goto out;
> > > >            }
> > > >            /*
> > > > @@ -484,8 +495,28 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, 
> > > > IOMMUTLBEntry *iotlb)
> > > >                             "0x%"HWADDR_PRIx", %p) = %d (%m)",
> > > >                             container, iova,
> > > >                             iotlb->addr_mask + 1, vaddr, ret);
> > > > +        } else {
> > > > +            VFIOIovaRange *iova_range;
> > > > +
> > > > +            iova_range = g_malloc0(sizeof(*iova_range));
> > > > +            iova_range->iova = iova;
> > > > +            iova_range->size = iotlb->addr_mask + 1;
> > > > +            iova_range->ram_addr = ram_addr;
> > > > +
> > > > +            QLIST_INSERT_HEAD(&giommu->iova_list, iova_range, next);
> > > >            }
> > > >        } else {
> > > > +        VFIOIovaRange *iova_range, *tmp;
> > > > +
> > > > +        QLIST_FOREACH_SAFE(iova_range, &giommu->iova_list, next, tmp) {
> > > > +            if (iova_range->iova >= iova &&
> > > > +                iova_range->iova + iova_range->size <= iova +
> > > > +                                                       iotlb->addr_mask + 1) {
> > > > +                QLIST_REMOVE(iova_range, next);
> > > > +                g_free(iova_range);
> > > > +            }
> > > > +        }
> > > > +
> > >
> > >
> > > This is some pretty serious overhead... can't we trigger a replay when
> > > migration is enabled to build this information then?
> >
> > Are you suggesting to call memory_region_iommu_replay() before
> > vfio_sync_dirty_bitmap(), which would call vfio_iommu_map_notify() where
> > iova list of mapping is maintained? Then in the notifer check if
> > migration_is_running() and container->dirty_pages_supported == true,
> > then only create iova mapping tree? In this case how would we know that
> > this is triggered by
> > vfio_sync_dirty_bitmap()
> >    -> memory_region_iommu_replay()
> > and we don't have to call vfio_dma_map()?
>
> memory_region_iommu_replay() calls a notifier of our choice, so we
> could create a notifier specifically for creating this tree when dirty
> logging is enabled.  Thanks,

This would also mean changes in intel_iommu.c such that it would walk 
through the iova_tree and call notifier for each entry in iova_tree. 
What about other platforms? We will have to handle such cases for AMD, 
ARM, PPC etc...?
I don't see replay callback for AMD, that would result in minimum IOMMU 
supported page size granularity walk - which is similar to that I tried 
to implement 2-3 versions back.
Does that mean doing such change would improve performance for Intel 
IOMMU but worsen for AMD/PPC?

I'm changing list to tree as first level of improvement in this patch.

Can we do the change you suggested above later as next level of improvement?

Thanks,
Kirti