Re: [PATCH 05/12] iommufd/hw_pagetable: Do not populate user-managed hw_pagetables

Baolu Lu
2023-03-10T12:52:09Z

On 2023/3/10 14:50, Nicolin Chen wrote:
> On Fri, Mar 10, 2023 at 10:25:10AM +0800, Baolu Lu wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 3/9/23 4:09 PM, Yi Liu wrote:
>>> From: Nicolin Chen <nicolinc@nvidia.com>
>>>
>>> A user-managed hw_pagetable does not need to get populated, since it is
>>> managed by a guest OS. Move the iopt_table_add_domain and list_add_tail
>>> calls into a helper, where the hwpt pointer will be redirected to its
>>> hwpt->parent if it's available.
>>>
>>> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>> ---
>>> drivers/iommu/iommufd/hw_pagetable.c | 20 ++++++++++++++++++--
>>> 1 file changed, 18 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
>>> index 16e92a1c150b..6e45ec0a66fa 100644
>>> --- a/drivers/iommu/iommufd/hw_pagetable.c
>>> +++ b/drivers/iommu/iommufd/hw_pagetable.c
>>> @@ -43,6 +43,23 @@ int iommufd_hw_pagetable_enforce_cc(struct iommufd_hw_pagetable *hwpt)
>>> return 0;
>>> }
>>>
>>> +static int iommufd_hw_pagetable_link_ioas(struct iommufd_hw_pagetable *hwpt)
>>> +{
>>> + int rc;
>>> +
>>> + if (hwpt->parent)
>>> + hwpt = hwpt->parent;
>>> +
>>> + if (!list_empty(&hwpt->hwpt_item))
>>> + return 0;
>>
>> What is above check for? Is it "the hwpt has already been inserted into
>> the hwpt list of its ioas in another place"?
>>
>> If so, is it possible that hwpt will be deleted from the list even when
>> this user hwpt is still linked to the ioas?
>
> It means that the hwpt is already linked to the ioas. And the
> hwpt_item can be only empty after a destroy().
>
> With that being said, after I think it through, perhaps Yi's
> previous change removing it might be better. So, it could be:
>
> -------------------------------------------------------------------------------
> + /*
> + * Only a parent hwpt needs to be linked to the IOAS. And a hwpt->parent
> + * must be linked to the IOAS already, when it's being allocated.
> + */
> if (hwpt->parent)
> - hwpt = hwpt->parent;
> -
> - if (!list_empty(&hwpt->hwpt_item))
> return 0;
>
> -------------------------------------------------------------------------------
>
> I was concerned about the case where a device gets attached to
> the nested hwpt without staging at the parent hwpt first. But,
> the link between the parent hwpt and the IOAS happened inside
> the allocation function now, not attach() any more.

Yes, it's clearer.

Best regards,
baolu