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

[Kirti Wankhede <kwankhede@nvidia.com>]

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