Hi zhangfei....@foxmail.com,
On Fri, 15 Apr 2022 19:52:03 +0800, "zhangfei....@foxmail.com"
<zhangfei....@foxmail.com> wrote:
> >>> A PASID might be still used even though it is freed on mm exit.
> >>>
> >>> process A:
> >>> sva_bind();
> >>> ioasid_alloc() = N; // Get PASID N for the mm
> >>> fork(): // spawn process B
> >>> exit();
> >>> ioasid_free(N);
> >>>
> >>> process B:
> >>> device uses PASID N -> failure
> >>> sva_unbind();
> >>>
> >>> Dave Hansen suggests to take a refcount on the mm whenever binding the
> >>> PASID to a device and drop the refcount on unbinding. The mm won't be
> >>> dropped if the PASID is still bound to it.
> >>>
> >>> Fixes: 701fac40384f ("iommu/sva: Assign a PASID to mm on PASID
> >>> allocation and free it on mm exit")
> >>>
Is process A's mm intended to be used by process B? Or you really should
use PASID N on process B's mm? If the latter, it may work for a while until
B changes mapping.
It seems you are just extending the life of a defunct mm?
Thanks,
Jacob
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