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

From: Kirti Wankhede <kwankhede@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: cohuck@redhat.com, cjia@nvidia.com, aik@ozlabs.ru,
	Zhengxiao.zx@Alibaba-inc.com, shuangtai.tst@alibaba-inc.com,
	qemu-devel@nongnu.org, peterx@redhat.com, eauger@redhat.com,
	yi.l.liu@intel.com, quintela@redhat.com, ziye.yang@intel.com,
	armbru@redhat.com, mlevitsk@redhat.com, pasic@linux.ibm.com,
	felipe@nutanix.com, zhi.a.wang@intel.com, kevin.tian@intel.com,
	yan.y.zhao@intel.com, dgilbert@redhat.com,
	changpeng.liu@intel.com, eskultet@redhat.com, Ken.Xue@amd.com,
	jonathan.davies@nutanix.com, pbonzini@redhat.com
Subject: Re: [PATCH v26 13/17] vfio: create mapped iova list when vIOMMU is enabled
Date: Mon, 19 Oct 2020 11:31:03 +0530	[thread overview]
Message-ID: <d7337283-72b6-3047-3c91-580697a63715@nvidia.com> (raw)
In-Reply-To: <20200925162316.53dbd2b0@x1.home>

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()?

> We're looking at
> potentially thousands of entries, so a list is probably also not a good
> choice. 

Changing it to tree.

Thanks,
Kirti

  I don't think it's acceptable to incur this even when not
> migrating (ie. the vast majority of the time).  Thanks,
> 
> Alex
> 
>>           ret = vfio_dma_unmap(container, iova, iotlb->addr_mask + 1);
>>           if (ret) {
>>               error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
>> @@ -642,6 +673,7 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>               g_free(giommu);
>>               goto fail;
>>           }
>> +        QLIST_INIT(&giommu->iova_list);
>>           QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
>>           memory_region_iommu_replay(giommu->iommu, &giommu->n);
>>   
>> @@ -740,6 +772,13 @@ static void vfio_listener_region_del(MemoryListener *listener,
>>           QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
>>               if (MEMORY_REGION(giommu->iommu) == section->mr &&
>>                   giommu->n.start == section->offset_within_region) {
>> +                VFIOIovaRange *iova_range, *tmp;
>> +
>> +                QLIST_FOREACH_SAFE(iova_range, &giommu->iova_list, next, tmp) {
>> +                    QLIST_REMOVE(iova_range, next);
>> +                    g_free(iova_range);
>> +                }
>> +
>>                   memory_region_unregister_iommu_notifier(section->mr,
>>                                                           &giommu->n);
>>                   QLIST_REMOVE(giommu, giommu_next);
>> @@ -1541,6 +1580,13 @@ static void vfio_disconnect_container(VFIOGroup *group)
>>           QLIST_REMOVE(container, next);
>>   
>>           QLIST_FOREACH_SAFE(giommu, &container->giommu_list, giommu_next, tmp) {
>> +            VFIOIovaRange *iova_range, *itmp;
>> +
>> +            QLIST_FOREACH_SAFE(iova_range, &giommu->iova_list, next, itmp) {
>> +                QLIST_REMOVE(iova_range, next);
>> +                g_free(iova_range);
>> +            }
>> +
>>               memory_region_unregister_iommu_notifier(
>>                       MEMORY_REGION(giommu->iommu), &giommu->n);
>>               QLIST_REMOVE(giommu, giommu_next);
>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
>> index 0a1651eda2d0..aa7524fe2cc5 100644
>> --- a/include/hw/vfio/vfio-common.h
>> +++ b/include/hw/vfio/vfio-common.h
>> @@ -89,11 +89,19 @@ typedef struct VFIOContainer {
>>       QLIST_ENTRY(VFIOContainer) next;
>>   } VFIOContainer;
>>   
>> +typedef struct VFIOIovaRange {
>> +    hwaddr iova;
>> +    size_t size;
>> +    ram_addr_t ram_addr;
>> +    QLIST_ENTRY(VFIOIovaRange) next;
>> +} VFIOIovaRange;
>> +
>>   typedef struct VFIOGuestIOMMU {
>>       VFIOContainer *container;
>>       IOMMUMemoryRegion *iommu;
>>       hwaddr iommu_offset;
>>       IOMMUNotifier n;
>> +    QLIST_HEAD(, VFIOIovaRange) iova_list;
>>       QLIST_ENTRY(VFIOGuestIOMMU) giommu_next;
>>   } VFIOGuestIOMMU;
>>   
> 