Re: [PATCH for 7.2? V2] vhost: fix vq dirty bitmap syncing when vIOMMU is enabled

[Eric Auger]

Hi Michael,

On 11/29/22 16:44, Michael S. Tsirkin wrote:
> On Tue, Nov 29, 2022 at 10:52:29AM +0100, Eric Auger wrote:
>> Hi Jason,
>>
>> On 11/29/22 05:02, Jason Wang wrote:
>>> When vIOMMU is enabled, the vq->used_phys is actually the IOVA not
>>> GPA. So we need to translate it to GPA before the syncing otherwise we
>>> may hit the following crash since IOVA could be out of the scope of
>>> the GPA log size. This could be noted when using virtio-IOMMU with
>>> vhost using 1G memory.
>>>
>>> Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support")
>>> Cc: qemu-stable@nongnu.org
>>> Tested-by: Lei Yang <leiyang@redhat.com>
>>> Reported-by: Yalan Zhang <yalzhang@redhat.com>
>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>> ---
>>> Changes since V1:
>>> - Fix the address calculation when used ring is not page aligned
>>> - Fix the length for each round of dirty bitmap syncing
>>> - Use LOG_GUEST_ERROR to log wrong used adddress
>>> - Various other tweaks
>>> ---
>>>  hw/virtio/vhost.c | 76 ++++++++++++++++++++++++++++++++++-------------
>>>  1 file changed, 56 insertions(+), 20 deletions(-)
>>>
>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>>> index d1c4c20b8c..0cd5f25fcb 100644
>>> --- a/hw/virtio/vhost.c
>>> +++ b/hw/virtio/vhost.c
>>> @@ -20,6 +20,7 @@
>>>  #include "qemu/range.h"
>>>  #include "qemu/error-report.h"
>>>  #include "qemu/memfd.h"
>>> +#include "qemu/log.h"
>>>  #include "standard-headers/linux/vhost_types.h"
>>>  #include "hw/virtio/virtio-bus.h"
>>>  #include "hw/virtio/virtio-access.h"
>>> @@ -106,6 +107,24 @@ static void vhost_dev_sync_region(struct vhost_dev 
>>> *dev,
>>>      }
>>>  }
>>>  
>>> +static bool vhost_dev_has_iommu(struct vhost_dev *dev)
>>> +{
>>> +    VirtIODevice *vdev = dev->vdev;
>>> +
>>> +    /*
>>> +     * For vhost, VIRTIO_F_IOMMU_PLATFORM means the backend support
>>> +     * incremental memory mapping API via IOTLB API. For platform that
>>> +     * does not have IOMMU, there's no need to enable this feature
>>> +     * which may cause unnecessary IOTLB miss/update transactions.
>>> +     */
>>> +    if (vdev) {
>>> +        return virtio_bus_device_iommu_enabled(vdev) &&
>>> +            virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
>>> +    } else {
>>> +        return false;
>>> +    }
>>> +}
>>> +
>>>  static int vhost_sync_dirty_bitmap(struct vhost_dev *dev,
>>>                                     MemoryRegionSection *section,
>>>                                     hwaddr first,
>>> @@ -137,8 +156,43 @@ static int vhost_sync_dirty_bitmap(struct vhost_dev 
>>> *dev,
>>>              continue;
>>>          }
>>>  
>>> -        vhost_dev_sync_region(dev, section, start_addr, end_addr, 
>>> vq->used_phys,
>>> -                              range_get_last(vq->used_phys, 
>>> vq->used_size));
>>> +        if (vhost_dev_has_iommu(dev)) {
>>> +            IOMMUTLBEntry iotlb;
>>> +            hwaddr used_phys = vq->used_phys, used_size = vq->used_size;
>>> +            hwaddr phys, s;
>>> +
>>> +            while (used_size) {
>>> +                rcu_read_lock();
>>> +                iotlb = address_space_get_iotlb_entry(dev->vdev->dma_as,
>>> +                                                      used_phys,
>>> +                                                      true, 
>>> MEMTXATTRS_UNSPECIFIED);
>>> +                rcu_read_unlock();
>>> +
>>> +                if (!iotlb.target_as) {
>>> +                    qemu_log_mask(LOG_GUEST_ERROR, "translation "
>>> +                                  "failure for used_phys %"PRIx64"\n", 
>>> used_phys);
>> looks weird to see translation of "used_phys" whereas it is an iova. At
>> least I would reword the msg
>>> +                    return -EINVAL;
>>> +                }
>>> +
>>> +                phys = iotlb.translated_addr + (used_phys & 
>>> iotlb.addr_mask);
>> you may use a local variable storing this offset =
>>
>> used_phys & iotlb.addr_mask
>>
>>> +
>>> +                /* Distance from start of used ring until last byte of
>>> +                   IOMMU page */
>> you can avoid checkpatch warnings here
>>> +                s = iotlb.addr_mask - (used_phys & iotlb.addr_mask);
>>> +                /* Size of used ring, or of the part of it until end
>>> +                   of IOMMU page */
>> and here
>>
>> I would suggest to rewrite this into
>> s =iotlb.addr_mask - (used_phys & iotlb.addr_mask) + 1
>> s = MIN(s, used_size);
> This does not work - if iotlb.addr_mask - (used_phys & iotlb.addr_mask)
> is all-ones then + 1 gives you 0 and MIN gives you 0.
> Theoretical but worth being safe here IMHO.
Ah OK, I should have read your previous discussion more thoroughly ...
Maybe just add a short comment then to justify the gym below and avoid
tempting sbdy else to rewrite it in a more common but wrong way.

Thanks

Eric
>
>
>>> +                s = MIN(s, used_size - 1) + 1;
>>> +
>>> +                vhost_dev_sync_region(dev, section, start_addr, end_addr, 
>>> phys,
>>> +                                      range_get_last(phys, s));
>>> +                used_size -= s;
>>> +                used_phys += s;
>>> +            }
>>> +        } else {
>>> +            vhost_dev_sync_region(dev, section, start_addr,
>>> +                                  end_addr, vq->used_phys,
>>> +                                  range_get_last(vq->used_phys, 
>>> vq->used_size));
>>> +        }
>>>      }
>>>      return 0;
>>>  }
>>> @@ -306,24 +360,6 @@ static inline void vhost_dev_log_resize(struct 
>>> vhost_dev *dev, uint64_t size)
>>>      dev->log_size = size;
>>>  }
>>>  
>>> -static bool vhost_dev_has_iommu(struct vhost_dev *dev)
>>> -{
>>> -    VirtIODevice *vdev = dev->vdev;
>>> -
>>> -    /*
>>> -     * For vhost, VIRTIO_F_IOMMU_PLATFORM means the backend support
>>> -     * incremental memory mapping API via IOTLB API. For platform that
>>> -     * does not have IOMMU, there's no need to enable this feature
>>> -     * which may cause unnecessary IOTLB miss/update transactions.
>>> -     */
>>> -    if (vdev) {
>>> -        return virtio_bus_device_iommu_enabled(vdev) &&
>>> -            virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
>>> -    } else {
>>> -        return false;
>>> -    }
>>> -}
>>> -
>>>  static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr,
>>>                                hwaddr *plen, bool is_write)
>>>  {
>> Besides,
>>
>> Tested-by: Eric Auger <eric.auger@redhat.com>
>>
>> Eric