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Date:   Tue, 28 Nov 2023 17:09:07 -0800
From:   Nicolin Chen <nicolinc@nvidia.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
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Subject: Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE
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On Tue, Nov 28, 2023 at 08:57:15PM -0400, Jason Gunthorpe wrote:
> On Tue, Nov 28, 2023 at 04:51:21PM -0800, Nicolin Chen wrote:
> > > > I also thought about making this out_driver_error_code per HW.
> > > > Yet, an error can be either per array or per entry/quest. The
> > > > array-related error should be reported in the array structure
> > > > that is a core uAPI, v.s. the per-HW entry structure. Though
> > > > we could still report an array error in the entry structure
> > > > at the first entry (or indexed by "array->entry_num")?
> > > >
> > > 
> > > why would there be an array error? array is just a software
> > > entity containing actual HW invalidation cmds. If there is
> > > any error with the array itself it should be reported via
> > > ioctl errno.
> > 
> > User array reading is a software operation, but kernel array
> > reading is a hardware operation that can raise an error when
> > the memory location to the array is incorrect or so.
> 
> Well, we shouldn't get into a situation like that.. By the time the HW
> got the address it should be valid.

Oh, that's true. I was trying to say that out_driver_error_code
was to mimic such a queue validation for user space if an error
happens to the array.

> > With that being said, I think errno (-EIO) could do the job,
> > as you suggested too.
> 
> Do we have any idea what HW failures can be generated by the commands
> this will execture? IIRC I don't remember seeing any smmu specific
> codes related to invalid invalidation? Everything is a valid input?

"7.1 Command queue errors" has the info.

Thanks
Nic