>-----Original Message-----
>From: Cédric Le Goater <[email protected]>
>Subject: Re: [PATCH 1/5] vfio/iommufd: Add framework code to support
>getting dirty bitmap before unmap
>
>On 9/22/25 05:17, Duan, Zhenzhong wrote:
>> Hi Cedric,
>>
>>> -----Original Message-----
>>> From: Cédric Le Goater <[email protected]>
>>> Subject: Re: [PATCH 1/5] vfio/iommufd: Add framework code to support
>>> getting dirty bitmap before unmap
>>>
>>> Hello Zhenzhong
>>>
>>> On 9/10/25 04:36, Zhenzhong Duan wrote:
>>>> Currently we support device and iommu dirty tracking, device dirty
>>>> tracking is preferred.
>>>>
>>>> Add the framework code in iommufd_cdev_unmap_one() to choose
>either
>>>> device or iommu dirty tracking, just like vfio_legacy_dma_unmap_one().
>>>
>>> I wonder if commit 567d7d3e6be5 ("vfio/common: Work around kernel
>>> overflow bug in DMA unmap") could be removed now to make the code
>>> common to both VFIO IOMMU Type1 and IOMMUFD backends.
>>
>> I am not clear if there is other reason to keep the workaround, but the
>original
>> kernel issue had been fixed with below commit:
>>
>> commit 58fec830fc19208354895d9832785505046d6c01
>> Author: Alex Williamson <[email protected]>
>> Date: Mon Jan 7 22:13:22 2019 -0700
>>
>> vfio/type1: Fix unmap overflow off-by-one
>>
>> The below referenced commit adds a test for integer overflow, but in
>> doing so prevents the unmap ioctl from ever including the last page
>of
>> the address space. Subtract one to compare to the last address of
>the
>> unmap to avoid the overflow and wrap-around.
>>
>> Fixes: 71a7d3d78e3c ("vfio/type1: silence integer overflow warning")
>> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1662291
>> Cc: [email protected] # v4.15+
>> Reported-by: Pei Zhang <[email protected]>
>> Debugged-by: Peter Xu <[email protected]>
>> Reviewed-by: Dan Carpenter <[email protected]>
>> Reviewed-by: Peter Xu <[email protected]>
>> Tested-by: Peter Xu <[email protected]>
>> Reviewed-by: Cornelia Huck <[email protected]>
>> Signed-off-by: Alex Williamson <[email protected]>
>>
>>>
>>> I asked Alex and Peter in another thread.
>>
>> Just curious on the answer, may I ask which thread?
>
>According to Alex, the QEMU workaround can be removed :
>
>https://lore.kernel.org/qemu-devel/20250919102447.748e17fe.alex.williams
>[email protected]/
>
>> btw: I just found unmapping in halves seems unnecessary as both backends
>of kernel side support unmap_all now.
>>
>> if (unmap_all) {
>> /* The unmap ioctl doesn't accept a full 64-bit span. */
>> Int128 llsize = int128_rshift(int128_2_64(), 1);
>>
>> ret = vfio_legacy_dma_unmap_one(bcontainer, 0,
>int128_get64(llsize),
>> iotlb);
>>
>> if (ret == 0) {
>> ret = vfio_legacy_dma_unmap_one(bcontainer,
>int128_get64(llsize),
>> int128_get64(llsize),
>iotlb);
>> }
>>
>> } else {
>> ret = vfio_legacy_dma_unmap_one(bcontainer, iova, size,
>iotlb);
>> }
>
>Good. So we can simply both backends it seems.
Will you handle them or not? I mean the workaround removing and unmapping_all
optimization.
Thanks
Zhenzhong
