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

[Alex Williamson]

On Thu, 25 Jun 2020 20:31:12 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> 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?

include/hw/qdev-core.h
struct DeviceState {
    ...
    bool allow_unplug_during_migration;

AIUI, the failover_pair_id device is likely to be a vfio-pci NIC,
otherwise they'd simply migrate the primary NIC, so there's a very good
chance that a user would configure a VM with a migratable mdev device
and an failover NIC so that they have high speed networking on either
end of the migration.
 
> _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.

We can't have unmaps while vCPUs are stopped, but I think the failover
code allows that we can be in the pre-copy phase where not all devices
support migration.  As coded here, it appears that dirty tracking of any
unmap while in that phase is lost.  Thanks,

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)",  
> >   
>