linux-kernel - Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT

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Date:   Tue, 28 Nov 2023 17:09:07 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
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        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>,
        "joao.m.martins@...cle.com" <joao.m.martins@...cle.com>,
        "Zeng, Xin" <xin.zeng@...el.com>,
        "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

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