Re: [PATCH v16 QEMU 14/16] vfio: Add vfio_listener_log_sync to mark dirty pages

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Alex Williamson (alex.williamson@redhat.com) wrote:
> On Wed, 25 Mar 2020 02:39:12 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> 
> > vfio_listener_log_sync gets list of dirty pages from container using
> > VFIO_IOMMU_GET_DIRTY_BITMAP ioctl and mark those pages dirty when all
> > devices are stopped and saving state.
> > Return early for the RAM block section of mapped MMIO region.
> > 
> > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > Reviewed-by: Neo Jia <cjia@nvidia.com>
> > ---
> >  hw/vfio/common.c     | 200 +++++++++++++++++++++++++++++++++++++++++++++++++--
> >  hw/vfio/trace-events |   1 +
> >  2 files changed, 196 insertions(+), 5 deletions(-)
> > 
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index 4a2f0d6a2233..6d41e1ac5c2f 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -29,6 +29,7 @@
> >  #include "hw/vfio/vfio.h"
> >  #include "exec/address-spaces.h"
> >  #include "exec/memory.h"
> > +#include "exec/ram_addr.h"
> >  #include "hw/hw.h"
> >  #include "qemu/error-report.h"
> >  #include "qemu/main-loop.h"
> > @@ -38,6 +39,7 @@
> >  #include "sysemu/reset.h"
> >  #include "trace.h"
> >  #include "qapi/error.h"
> > +#include "migration/migration.h"
> >  
> >  VFIOGroupList vfio_group_list =
> >      QLIST_HEAD_INITIALIZER(vfio_group_list);
> > @@ -288,6 +290,28 @@ const MemoryRegionOps vfio_region_ops = {
> >  };
> >  
> >  /*
> > + * Device state interfaces
> > + */
> > +
> > +static bool vfio_devices_are_stopped_and_saving(void)
> > +{
> > +    VFIOGroup *group;
> > +    VFIODevice *vbasedev;
> > +
> > +    QLIST_FOREACH(group, &vfio_group_list, next) {
> > +        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;
> > +            }
> > +        }
> > +    }
> > +    return true;
> > +}
> > +
> > +/*
> >   * DMA - Mapping and unmapping for the "type1" IOMMU interface used on x86
> >   */
> >  static int vfio_dma_unmap(VFIOContainer *container,
> > @@ -408,8 +432,8 @@ 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;
> > @@ -440,9 +464,17 @@ 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;
> >  }
> >  
> > @@ -467,7 +499,7 @@ 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)) {
> > +        if (!vfio_get_xlat_addr(iotlb, &vaddr, NULL, &read_only)) {
> >              goto out;
> >          }
> >          /*
> > @@ -813,9 +845,167 @@ static void vfio_listener_region_del(MemoryListener *listener,
> >      }
> >  }
> >  
> > +static int vfio_get_dirty_bitmap(MemoryListener *listener,
> > +                                 MemoryRegionSection *section)
> > +{
> > +    VFIOContainer *container = container_of(listener, VFIOContainer, listener);
> > +    VFIOGuestIOMMU *giommu;
> > +    IOMMUTLBEntry iotlb;
> > +    hwaddr granularity, address_limit, iova;
> > +    int ret;
> > +
> > +    if (memory_region_is_iommu(section->mr)) {
> > +        QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
> > +            if (MEMORY_REGION(giommu->iommu) == section->mr &&
> > +                giommu->n.start == section->offset_within_region) {
> > +                break;
> > +            }
> > +        }
> > +
> > +        if (!giommu) {
> > +            return -EINVAL;
> > +        }
> > +    }
> > +
> > +    if (memory_region_is_iommu(section->mr)) {
> > +        granularity = memory_region_iommu_get_min_page_size(giommu->iommu);
> > +
> > +        address_limit = MIN(int128_get64(section->size),
> > +                            memory_region_iommu_get_address_limit(giommu->iommu,
> > +                                                 int128_get64(section->size)));
> > +    } else {
> > +        granularity = memory_region_size(section->mr);
> > +        address_limit = int128_get64(section->size);
> > +    }
> > +
> > +    iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
> > +
> > +    RCU_READ_LOCK_GUARD();
> > +
> > +    while (iova < address_limit) {
> > +        struct vfio_iommu_type1_dirty_bitmap *dbitmap;
> > +        struct vfio_iommu_type1_dirty_bitmap_get *range;
> > +        ram_addr_t start, pages;
> > +        uint64_t iova_xlat, size;
> > +
> > +        if (memory_region_is_iommu(section->mr)) {
> > +            iotlb = address_space_get_iotlb_entry(container->space->as, iova,
> > +                                                 true, MEMTXATTRS_UNSPECIFIED);
> > +            if ((iotlb.target_as == NULL) || (iotlb.addr_mask == 0)) {
> > +                if ((iova + granularity) < iova) {
> > +                    break;
> > +                }
> > +                iova += granularity;
> > +                continue;
> > +            }
> > +            iova_xlat = iotlb.iova + giommu->iommu_offset;
> > +            size = iotlb.addr_mask + 1;
> > +        } else {
> > +            iova_xlat = iova;
> > +            size = address_limit;
> > +        }
> > +
> > +        dbitmap = g_malloc0(sizeof(*dbitmap) + sizeof(*range));
> > +        if (!dbitmap) {
> 
> AIUI, QEMU aborts if this fails, so no need to check.  Because reasons.

It does if you use g_malloc0; however if the data is large you can
use g_try_malloc0 and then it will return NULL and you can fail the
migration rather than nuking the VM.
(We often argue whether it's worth testing or not, I think generally 
if the size is 'large' or user defined then use try, if it's small
then assume it works.  We've never defined small or large; but somewhere
around a few pages is about right.

Dave

> > +            return -ENOMEM;
> > +        }
> > +
> > +        dbitmap->argsz = sizeof(*dbitmap) + sizeof(*range);
> > +        dbitmap->flags = VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP;
> > +        range = (struct vfio_iommu_type1_dirty_bitmap_get *)&dbitmap->data;
> > +        range->iova = iova_xlat;
> > +        range->size = size;
> > +
> > +        /*
> > +         * cpu_physical_memory_set_dirty_lebitmap() expects pages in bitmap of
> > +         * TARGET_PAGE_SIZE to mark those dirty. Hence set bitmap's pgsize to
> > +         * TARGET_PAGE_SIZE.
> > +         */
> > +        range->bitmap.pgsize = TARGET_PAGE_SIZE;
> > +
> > +        /*
> > +         * Comment from kvm_physical_sync_dirty_bitmap() since same applies here
> > +         * XXX bad kernel interface alert
> > +         * For dirty bitmap, kernel allocates array of size aligned to
> > +         * bits-per-long.  But for case when the kernel is 64bits and
> > +         * the userspace is 32bits, userspace can't align to the same
> > +         * bits-per-long, since sizeof(long) is different between kernel
> > +         * and user space.  This way, userspace will provide buffer which
> > +         * may be 4 bytes less than the kernel will use, resulting in
> > +         * userspace memory corruption (which is not detectable by valgrind
> > +         * too, in most cases).
> > +         * So for now, let's align to 64 instead of HOST_LONG_BITS here, in
> > +         * a hope that sizeof(long) won't become >8 any time soon.
> > +         */
> 
> This seems like the problem we've avoided by defining our bitmap as an
> array of u64s rather than an array of longs.  Does this comment really
> still apply?
> 
> > +
> > +        pages = TARGET_PAGE_ALIGN(range->size) >> TARGET_PAGE_BITS;
> > +        range->bitmap.size = ROUND_UP(pages, 64) / 8;
> 
> ROUND_UP(npages/8, sizeof(u64))?
> 
> > +        range->bitmap.data = g_malloc0(range->bitmap.size);
> 
> We don't require this to be pre-zero'd currently.
> 
> > +        if (range->bitmap.data == NULL) {
> 
> Same as above.  Seems strange to me too.
> 
> > +            error_report("Error allocating bitmap of size 0x%llx",
> > +                         range->bitmap.size);
> > +            ret = -ENOMEM;
> > +            goto err_out;
> > +        }
> > +
> > +        ret = ioctl(container->fd, VFIO_IOMMU_DIRTY_PAGES, dbitmap);
> > +        if (ret) {
> > +            error_report("Failed to get dirty bitmap for iova: 0x%llx "
> > +                         "size: 0x%llx err: %d",
> > +                         range->iova, range->size, errno);
> > +            goto err_out;
> > +        }
> > +
> > +        if (memory_region_is_iommu(section->mr)) {
> > +            if (!vfio_get_xlat_addr(&iotlb, NULL, &start, NULL)) {
> > +                ret = -EINVAL;
> > +                goto err_out;
> > +            }
> > +        } else {
> > +            start = memory_region_get_ram_addr(section->mr) +
> > +                    section->offset_within_region + iova -
> > +                    TARGET_PAGE_ALIGN(section->offset_within_address_space);
> > +        }
> > +
> > +        cpu_physical_memory_set_dirty_lebitmap((uint64_t *)range->bitmap.data,
> > +                                               start, pages);
> > +
> > +        trace_vfio_get_dirty_bitmap(container->fd, range->iova, range->size,
> > +                                    range->bitmap.size, start);
> > +err_out:
> > +        g_free(range->bitmap.data);
> > +        g_free(dbitmap);
> > +
> > +        if (ret) {
> > +            return ret;
> > +        }
> > +
> > +        if ((iova + size) < iova) {
> > +            break;
> > +        }
> > +
> > +        iova += size;
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +static void vfio_listerner_log_sync(MemoryListener *listener,
> > +        MemoryRegionSection *section)
> > +{
> > +    if (vfio_listener_skipped_section(section)) {
> > +        return;
> > +    }
> > +
> > +    if (vfio_devices_are_stopped_and_saving()) {
> > +        vfio_get_dirty_bitmap(listener, section);
> > +    }
> > +}
> > +
> >  static const MemoryListener vfio_memory_listener = {
> >      .region_add = vfio_listener_region_add,
> >      .region_del = vfio_listener_region_del,
> > +    .log_sync = vfio_listerner_log_sync,
> >  };
> >  
> >  static void vfio_listener_release(VFIOContainer *container)
> > diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> > index ac065b559f4e..bc8f35ee9356 100644
> > --- a/hw/vfio/trace-events
> > +++ b/hw/vfio/trace-events
> > @@ -160,3 +160,4 @@ vfio_save_complete_precopy(char *name) " (%s)"
> >  vfio_load_device_config_state(char *name) " (%s)"
> >  vfio_load_state(char *name, uint64_t data) " (%s) data 0x%"PRIx64
> >  vfio_load_state_device_data(char *name, uint64_t data_offset, uint64_t data_size) " (%s) Offset 0x%"PRIx64" size 0x%"PRIx64
> > +vfio_get_dirty_bitmap(int fd, uint64_t iova, uint64_t size, uint64_t bitmap_size, uint64_t start) "container fd=%d, iova=0x%"PRIx64" size= 0x%"PRIx64" bitmap_size=0x%"PRIx64" start=0x%"PRIx64
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK