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Date:   Fri, 11 Aug 2023 10:40:15 +0800
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Cc:     baolu.lu@linux.intel.com, Joerg Roedel <joro@8bytes.org>,
        Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Nicolin Chen <nicolinc@nvidia.com>,
        Yi Liu <yi.l.liu@intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        iommu@lists.linux.dev, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 12/12] iommu: Add helper to set iopf handler for domain
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To:     Jason Gunthorpe <jgg@ziepe.ca>
References: <20230727054837.147050-1-baolu.lu@linux.intel.com>
 <20230727054837.147050-13-baolu.lu@linux.intel.com>
 <ZNU4Hio8oAHH8RLn@ziepe.ca>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <ZNU4Hio8oAHH8RLn@ziepe.ca>
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On 2023/8/11 3:18, Jason Gunthorpe wrote:
> On Thu, Jul 27, 2023 at 01:48:37PM +0800, Lu Baolu wrote:
>> To avoid open code everywhere.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   include/linux/iommu.h | 11 ++++++++++-
>>   drivers/iommu/iommu.c | 20 ++++++++++++++++++--
>>   2 files changed, 28 insertions(+), 3 deletions(-)
> 
> Seems like overkill at this point..
> 
> Also, I think this is probably upside down.
> 
> We want to create the domains as fault enabled in the first place.
> 
> A fault enabled domain should never be attached to something that
> cannot support faults. It should also not support changing the fault
> handler while it exists.
> 
> Thus at the creation point would be the time to supply the fault handler
> as part of requesting faulting.
> 
> Taking an existing domain and making it faulting enabled is going to
> be really messy in all the corner cases.

Yes. Agreed.

> 
> My advice (and Robin will probably hate me), is to define a new op:
> 
> struct domain_alloc_paging_args {
>         struct fault_handler *fault_handler;
>         void *fault_data
> };
> 
> struct iommu_domain *domain_alloc_paging2(struct device *dev, struct
>         domain_alloc_paging_args *args)
> 
> The point would be to leave the majority of drivers using the
> simplified, core assisted, domain_alloc_paging() interface and they
> just don't have to touch any of this stuff at all.
> 
> Obviously if handler is given then the domain will be initialized as
> faulting.

Perhaps we also need an internal helper for iommu drivers to check the
iopf capability of the domain.

Best regards,
baolu