On 2021/5/19 2:58, Alex Williamson wrote:

On Fri, 9 Apr 2021 11:44:13 +0800
Shenming Lu [off-list ref] wrote:

quoted

This patch follows the discussion here:

https://lore.kernel.org/linux-acpi/YAaxjmJW+ZMvrhac@myrica/ (local)

Besides SVA/vSVA, such as VFIO may also enable (2nd level) IOPF to remove
pinning restriction. In order to better support more scenarios of using
device faults, we extend iommu_register_fault_handler() with flags and
introduce FAULT_REPORT_ to describe the device fault reporting capability
under a specific configuration.

Note that we don't further distinguish recoverable and unrecoverable faults
by flags in the fault reporting cap, having PAGE_FAULT_REPORT_ +
UNRECOV_FAULT_REPORT_ seems not a clean way.

In addition, still take VFIO as an example, in nested mode, the 1st level
and 2nd level fault reporting may be configured separately and currently
each device can only register one iommu dev fault handler, so we add a
handler update interface for this.

IIUC, you're introducing flags for the fault handler callout, which
essentially allows the IOMMU layer to filter which types of faults the
handler can receive.  You then need an update function to modify those
flags.  Why can't the handler itself perform this filtering?  For
instance in your vfio example, the handler registered by the type1
backend could itself return fault until the fault transfer path to the
device driver is established.  Thanks,

As discussed in [1]:

In nested IOPF, we have to figure out whether a fault comes from L1 or L2.
A SMMU stall event comes with this information, but a PRI page request doesn't.
The IOMMU driver can walk the page tables to find out the level information.
If the walk terminates at L1, further inject to the guest. Otherwise fix the
fault at L2 in VFIO. It's not efficient compared to hardware-provided info.

And in pinned case, if VFIO can tell the IOMMU driver that no L2 fault is
expected, there is no need to walk the page tables in the IOMMU driver?

[1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20210108145217.2254447-4-jean-philippe@linaro.org/

Thanks,
Shenming

Alex

.