Re: [PATCH QEMU v25 15/17] vfio: Add ioctl to get dirty pages bitmap during dma unmap.

[Kirti Wankhede <kwankhede@nvidia.com>]

On 6/25/2020 12:26 AM, Alex Williamson wrote:
> On Sun, 21 Jun 2020 01:51:24 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> 
>> With vIOMMU, IO virtual address range can get unmapped while in pre-copy
>> phase of migration. In that case, unmap ioctl should return pages pinned
>> in that range and QEMU should find its correcponding guest physical
>> addresses and report those dirty.
>>
>> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   hw/vfio/common.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
>>   1 file changed, 81 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 0518cf228ed5..a06b8f2f66e2 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -311,11 +311,83 @@ static bool vfio_devices_are_stopped_and_saving(void)
>>       return true;
>>   }
>>   
>> +static bool vfio_devices_are_running_and_saving(void)
>> +{
>> +    VFIOGroup *group;
>> +    VFIODevice *vbasedev;
>> +
>> +    QLIST_FOREACH(group, &vfio_group_list, next) {
> 
> Same as previous, I'm curious if we should instead be looking at
> container granularity.  It especially seems to make sense here where
> we're unmapping from a container, so iterating every device in every
> group seems excessive.
> 

changing it with container argument.

>> +        QLIST_FOREACH(vbasedev, &group->device_list, next) {
>> +            if ((vbasedev->device_state & VFIO_DEVICE_STATE_SAVING) &&
>> +                (vbasedev->device_state & VFIO_DEVICE_STATE_RUNNING)) {
>> +                continue;
>> +            } else {
>> +                return false;
>> +            }
> 
> I'm also not sure about the polarity of this function, should it be if
> any device is _SAVING we should report the dirty bitmap?  For example,
> what if we have a set of paried failover NICs where we intend to unplug
> one just prior to stopping the devices, aren't we going to lose dirtied
> pages with this logic that they all must be running and saving?  Thanks,
> 

If migration is initiated, is device unplug allowed? Ideally it 
shouldn't. If it is, then how QEMU handles data stream of device which 
doesn't exist at destination?

_SAVING flag is set during pre-copy and stop-and-copy phase. Here we 
only want to track pages which are unmapped during pre-copy phase, i.e. 
when vCPU are running. In case of VM suspend /saveVM, there is no 
pre-copy phase, but ideally we shouldn't see unmaps when vCPUs are 
stopped, right? But still for safer side, since we know exact phase, I 
would prefer to check for _SAVING and _RUNNING flags.

Thanks,
Kirti


> Alex
> 
>> +        }
>> +    }
>> +    return true;
>> +}
>> +
>> +static int vfio_dma_unmap_bitmap(VFIOContainer *container,
>> +                                 hwaddr iova, ram_addr_t size,
>> +                                 IOMMUTLBEntry *iotlb)
>> +{
>> +    struct vfio_iommu_type1_dma_unmap *unmap;
>> +    struct vfio_bitmap *bitmap;
>> +    uint64_t pages = TARGET_PAGE_ALIGN(size) >> TARGET_PAGE_BITS;
>> +    int ret;
>> +
>> +    unmap = g_malloc0(sizeof(*unmap) + sizeof(*bitmap));
>> +
>> +    unmap->argsz = sizeof(*unmap) + sizeof(*bitmap);
>> +    unmap->iova = iova;
>> +    unmap->size = size;
>> +    unmap->flags |= VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP;
>> +    bitmap = (struct vfio_bitmap *)&unmap->data;
>> +
>> +    /*
>> +     * cpu_physical_memory_set_dirty_lebitmap() expects pages in bitmap of
>> +     * TARGET_PAGE_SIZE to mark those dirty. Hence set bitmap_pgsize to
>> +     * TARGET_PAGE_SIZE.
>> +     */
>> +
>> +    bitmap->pgsize = TARGET_PAGE_SIZE;
>> +    bitmap->size = ROUND_UP(pages, sizeof(__u64) * BITS_PER_BYTE) /
>> +                   BITS_PER_BYTE;
>> +
>> +    if (bitmap->size > container->max_dirty_bitmap_size) {
>> +        error_report("UNMAP: Size of bitmap too big 0x%llx", bitmap->size);
>> +        ret = -E2BIG;
>> +        goto unmap_exit;
>> +    }
>> +
>> +    bitmap->data = g_try_malloc0(bitmap->size);
>> +    if (!bitmap->data) {
>> +        ret = -ENOMEM;
>> +        goto unmap_exit;
>> +    }
>> +
>> +    ret = ioctl(container->fd, VFIO_IOMMU_UNMAP_DMA, unmap);
>> +    if (!ret) {
>> +        cpu_physical_memory_set_dirty_lebitmap((uint64_t *)bitmap->data,
>> +                iotlb->translated_addr, pages);
>> +    } else {
>> +        error_report("VFIO_UNMAP_DMA with DIRTY_BITMAP : %m");
>> +    }
>> +
>> +    g_free(bitmap->data);
>> +unmap_exit:
>> +    g_free(unmap);
>> +    return ret;
>> +}
>> +
>>   /*
>>    * DMA - Mapping and unmapping for the "type1" IOMMU interface used on x86
>>    */
>>   static int vfio_dma_unmap(VFIOContainer *container,
>> -                          hwaddr iova, ram_addr_t size)
>> +                          hwaddr iova, ram_addr_t size,
>> +                          IOMMUTLBEntry *iotlb)
>>   {
>>       struct vfio_iommu_type1_dma_unmap unmap = {
>>           .argsz = sizeof(unmap),
>> @@ -324,6 +396,11 @@ static int vfio_dma_unmap(VFIOContainer *container,
>>           .size = size,
>>       };
>>   
>> +    if (iotlb && container->dirty_pages_supported &&
>> +        vfio_devices_are_running_and_saving()) {
>> +        return vfio_dma_unmap_bitmap(container, iova, size, iotlb);
>> +    }
>> +
>>       while (ioctl(container->fd, VFIO_IOMMU_UNMAP_DMA, &unmap)) {
>>           /*
>>            * The type1 backend has an off-by-one bug in the kernel (71a7d3d78e3c
>> @@ -371,7 +448,7 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr iova,
>>        * the VGA ROM space.
>>        */
>>       if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0 ||
>> -        (errno == EBUSY && vfio_dma_unmap(container, iova, size) == 0 &&
>> +        (errno == EBUSY && vfio_dma_unmap(container, iova, size, NULL) == 0 &&
>>            ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0)) {
>>           return 0;
>>       }
>> @@ -542,7 +619,7 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
>>               }
>>           }
>>   
>> -        ret = vfio_dma_unmap(container, iova, iotlb->addr_mask + 1);
>> +        ret = vfio_dma_unmap(container, iova, iotlb->addr_mask + 1, iotlb);
>>           if (ret) {
>>               error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
>>                            "0x%"HWADDR_PRIx") = %d (%m)",
>> @@ -853,7 +930,7 @@ static void vfio_listener_region_del(MemoryListener *listener,
>>       }
>>   
>>       if (try_unmap) {
>> -        ret = vfio_dma_unmap(container, iova, int128_get64(llsize));
>> +        ret = vfio_dma_unmap(container, iova, int128_get64(llsize), NULL);
>>           if (ret) {
>>               error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
>>                            "0x%"HWADDR_PRIx") = %d (%m)",
>