Re: [PATCH 3/5] vfio/iommufd: Add IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR flag support

["Cédric Le Goater" <clg@redhat.com>]

On 9/22/25 07:49, Duan, Zhenzhong wrote:
> Hi Joao,
> 
>> -----Original Message-----
>> From: Joao Martins <joao.m.martins@oracle.com>
>> Subject: Re: [PATCH 3/5] vfio/iommufd: Add
>> IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR flag support
>>
>> On 10/09/2025 03:36, Zhenzhong Duan wrote:
>>> Pass IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR when doing the last
>> dirty
>>> bitmap query right before unmap, no PTEs flushes. This accelerates the
>>> query without issue because unmap will tear down the mapping anyway.
>>>
>>> Add a new element dirty_tracking_flags in VFIOIOMMUFDContainer to
>>> be used for the flags of iommufd dirty tracking. Currently it is
>>> set to either IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR or 0 based on
>>> the scenario.
>>>
>>> Co-developed-by: Joao Martins <joao.m.martins@oracle.com>
>>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>> Tested-by: Xudong Hao <xudong.hao@intel.com>
>>> Tested-by: Giovannio Cabiddu <giovanni.cabiddu@intel.com>
>>> ---
>>>   hw/vfio/vfio-iommufd.h   | 1 +
>>>   include/system/iommufd.h | 2 +-
>>>   backends/iommufd.c       | 5 +++--
>>>   hw/vfio/iommufd.c        | 6 +++++-
>>>   backends/trace-events    | 2 +-
>>>   5 files changed, 11 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/hw/vfio/vfio-iommufd.h b/hw/vfio/vfio-iommufd.h
>>> index 07ea0f4304..e0af241c75 100644
>>> --- a/hw/vfio/vfio-iommufd.h
>>> +++ b/hw/vfio/vfio-iommufd.h
>>> @@ -26,6 +26,7 @@ typedef struct VFIOIOMMUFDContainer {
>>>       VFIOContainerBase bcontainer;
>>>       IOMMUFDBackend *be;
>>>       uint32_t ioas_id;
>>> +    uint64_t dirty_tracking_flags;
>>>       QLIST_HEAD(, VFIOIOASHwpt) hwpt_list;
>>>   } VFIOIOMMUFDContainer;
>>>
>>> diff --git a/include/system/iommufd.h b/include/system/iommufd.h
>>> index c9c72ffc45..63898e7b0d 100644
>>> --- a/include/system/iommufd.h
>>> +++ b/include/system/iommufd.h
>>> @@ -64,7 +64,7 @@ bool
>> iommufd_backend_set_dirty_tracking(IOMMUFDBackend *be, uint32_t
>> hwpt_id,
>>>   bool iommufd_backend_get_dirty_bitmap(IOMMUFDBackend *be,
>> uint32_t hwpt_id,
>>>                                         uint64_t iova, ram_addr_t
>> size,
>>>                                         uint64_t page_size,
>> uint64_t *data,
>>> -                                      Error **errp);
>>> +                                      uint64_t flags, Error
>> **errp);
>>>   bool iommufd_backend_invalidate_cache(IOMMUFDBackend *be,
>> uint32_t id,
>>>                                         uint32_t data_type,
>> uint32_t entry_len,
>>>                                         uint32_t *entry_num, void
>> *data,
>>> diff --git a/backends/iommufd.c b/backends/iommufd.c
>>> index 2a33c7ab0b..3c4f6157e2 100644
>>> --- a/backends/iommufd.c
>>> +++ b/backends/iommufd.c
>>> @@ -361,7 +361,7 @@ bool
>> iommufd_backend_get_dirty_bitmap(IOMMUFDBackend *be,
>>>                                         uint32_t hwpt_id,
>>>                                         uint64_t iova, ram_addr_t
>> size,
>>>                                         uint64_t page_size,
>> uint64_t *data,
>>> -                                      Error **errp)
>>> +                                      uint64_t flags, Error **errp)
>>>   {
>>>       int ret;
>>>       struct iommu_hwpt_get_dirty_bitmap get_dirty_bitmap = {
>>> @@ -371,11 +371,12 @@ bool
>> iommufd_backend_get_dirty_bitmap(IOMMUFDBackend *be,
>>>           .length = size,
>>>           .page_size = page_size,
>>>           .data = (uintptr_t)data,
>>> +        .flags = flags,
>>>       };
>>>
>>>       ret = ioctl(be->fd, IOMMU_HWPT_GET_DIRTY_BITMAP,
>> &get_dirty_bitmap);
>>>       trace_iommufd_backend_get_dirty_bitmap(be->fd, hwpt_id, iova,
>> size,
>>> -                                           page_size, ret ? errno :
>> 0);
>>> +                                           flags, page_size, ret ?
>> errno : 0);
>>>       if (ret) {
>>>           error_setg_errno(errp, errno,
>>>                            "IOMMU_HWPT_GET_DIRTY_BITMAP
>> (iova: 0x%"HWADDR_PRIx
>>> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
>>> index 0057488ce9..c897aa6b17 100644
>>> --- a/hw/vfio/iommufd.c
>>> +++ b/hw/vfio/iommufd.c
>>> @@ -62,7 +62,7 @@ static int iommufd_cdev_unmap_one(const
>> VFIOContainerBase *bcontainer,
>>>                                     hwaddr iova, ram_addr_t size,
>>>                                     IOMMUTLBEntry *iotlb)
>>>   {
>>> -    const VFIOIOMMUFDContainer *container =
>>> +    VFIOIOMMUFDContainer *container =
>>>           container_of(bcontainer, VFIOIOMMUFDContainer,
>> bcontainer);
>>>       bool need_dirty_sync = false;
>>>       Error *local_err = NULL;
>>> @@ -73,9 +73,12 @@ static int iommufd_cdev_unmap_one(const
>> VFIOContainerBase *bcontainer,
>>>       if (iotlb && vfio_container_dirty_tracking_is_started(bcontainer)) {
>>>           if
>> (!vfio_container_devices_dirty_tracking_is_supported(bcontainer) &&
>>>               bcontainer->dirty_pages_supported) {
>>> +            container->dirty_tracking_flags =
>>> +
>> IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR;
>>>               ret = vfio_container_query_dirty_bitmap(bcontainer, iova,
>> size,
>>>
>> iotlb->translated_addr,
>>>
>> &local_err);
>>> +            container->dirty_tracking_flags = 0;
>>
>> Why not changing vfio_container_query_dirty_bitmap to pass a flags too, like
>> the
>> original patches? This is a little unnecssary odd style to pass a flag via
>> container structure rather and then clearing.
> 
> Just want to be simpler, original patch introduced a new parameter to almost all
> variants of *_query_dirty_bitmap() while the flags parameter is only used by
> IOMMUFD backend when doing unmap_bitmap. Currently we already have three
> backends, legacy VFIO, IOMMUFD and VFIO-user, only IOMMUFD need the flag.
> 
> I take container->dirty_tracking_flags as a notification mechanism, so set it before
> vfio_container_query_dirty_bitmap() and clear it thereafter. Maybe clearing it in
> iommufd_query_dirty_bitmap() is easier to be acceptable?
> 
>>
>> Part of the reason the original series had a VFIO_GET_DIRTY_NO_FLUSH for
>> generic
>> container abstraction was to not mix IOMMUFD UAPI specifics into base
>> container
>> API. Then in getting a VFIO_GET_DIRTY_NO_FLUSH, then type1 backend
>> could just
>> ignore the flag, while IOMMUFD translates it to
>> IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR
> 
> I did port original patch https://github.com/yiliu1765/qemu/commit/99f83595d79d2e4170c9e456cf1a7b9521bd4f80
> But it looks complex to have 'flags' parameter everywhere.
I think I would prefer like Joao to avoid caching information if possible
but I haven't check closely the mess it would introduce in the code. Let
me check.

Thanks,

C.