Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

Baolu Lu
2024-05-08T10:05:11Z

On 2024/5/8 8:11, Jason Gunthorpe wrote:
> On Tue, Apr 30, 2024 at 10:57:06PM +0800, Lu Baolu wrote:
>> diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
>> index ae65e0b85d69..1a0450a83bd0 100644
>> --- a/drivers/iommu/iommu-priv.h
>> +++ b/drivers/iommu/iommu-priv.h
>> @@ -36,6 +36,10 @@ struct iommu_attach_handle {
>> struct device *dev;
>> refcount_t users;
>> };
>> + /* attach data for IOMMUFD */
>> + struct {
>> + void *idev;
>> + };
> We can use a proper type here, just forward declare it.
>
> But this sequence in the other patch:
>
> + ret = iommu_attach_group(hwpt->domain, idev->igroup->group);
> + if (ret) {
> + iommufd_fault_iopf_disable(idev);
> + return ret;
> + }
> +
> + handle = iommu_attach_handle_get(idev->igroup->group, IOMMU_NO_PASID, 0);
> + handle->idev = idev;
>
> Is why I was imagining the caller would allocate, because now we have
> the issue that a fault capable domain was installed into the IOMMU
> before it's handle could be fully setup, so we have a race where a
> fault could come in right between those things. Then what happens?
> I suppose we can retry the fault and by the time it comes back the
> race should resolve. A bit ugly I suppose.

You are right. It makes more sense if the attached data is allocated and
managed by the caller. I will go in this direction and update my series.
I will also consider other review comments you have given in other
places.

Best regards,
baolu