On 9/13/23 10:34 AM, Tian, Kevin wrote:
From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
Sent: Monday, September 11, 2023 8:46 PM
On 2023/9/11 14:57, Tian, Kevin wrote:
From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
Sent: Tuesday, September 5, 2023 1:24 PM
Hi Kevin,
I am trying to address this issue in below patch. Does it looks sane to
you?
iommu: Consolidate per-device fault data management
The per-device fault data is a data structure that is used to store
information about faults that occur on a device. This data is allocated
when IOPF is enabled on the device and freed when IOPF is disabled. The
data is used in the paths of iopf reporting, handling, responding, and
draining.
The fault data is protected by two locks:
- dev->iommu->lock: This lock is used to protect the allocation and
freeing of the fault data.
- dev->iommu->fault_parameter->lock: This lock is used to protect the
fault data itself.
Improve the iopf code to enforce this lock mechanism and add a
reference
counter in the fault data to avoid use-after-free issue.
Can you elaborate the use-after-free issue and why a new user count
is required?
I was concerned that when iommufd uses iopf, page fault report/response
may occur simultaneously with enable/disable PRI.
Currently, this is not an issue as the enable/disable PRI is in its own
path. In the future, we may discard this interface and enable PRI when
attaching the first PRI-capable domain, and disable it when detaching
the last PRI-capable domain.
Then let's not do it now until there is a real need after you have a
thorough design for iommufd.
Okay, fair enough.
btw a Fix tag is required given this mislocking issue has been there for
quite some time...
I don't see any real issue fixed by this change. It's only a lock
refactoring after the code refactoring and preparing it for iommufd use.
Perhaps I missed anything?
mislocking already exists today for the partial list:
- iommu_queue_iopf() uses dev->iommu->lock;
- iopf_queue_discard_partial() uses queue->lock;
So, if it's worth it, let me try splitting a fix patch.
Best regards,
baolu
