linux-kernel - Re: [PATCH v10 10/12] iommu: Prepare IOMMU domain for IOPF

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Date:   Sun, 24 Jul 2022 22:04:50 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v10 10/12] iommu: Prepare IOMMU domain for IOPF

On 2022/7/23 22:33, Jason Gunthorpe wrote:
> On Tue, Jul 05, 2022 at 01:07:08PM +0800, Lu Baolu wrote:
>> This adds some mechanisms around the iommu_domain so that the I/O page
>> fault handling framework could route a page fault to the domain and
>> call the fault handler from it.
>>
>> Add pointers to the page fault handler and its private data in struct
>> iommu_domain. The fault handler will be called with the private data
>> as a parameter once a page fault is routed to the domain. Any kernel
>> component which owns an iommu domain could install handler and its
>> private parameter so that the page fault could be further routed and
>> handled.
>>
>> This also prepares the SVA implementation to be the first consumer of
>> the per-domain page fault handling model. The I/O page fault handler
>> for SVA is copied to the SVA file with mmget_not_zero() added before
>> mmap_read_lock().
>>
>> Suggested-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> Reviewed-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
>> Tested-by: Zhangfei Gao <zhangfei.gao@...aro.org>
>> Tested-by: Tony Zhu <tony.zhu@...el.com>
>> ---
>>   include/linux/iommu.h         |  3 ++
>>   drivers/iommu/iommu-sva-lib.h |  8 +++++
>>   drivers/iommu/io-pgfault.c    |  7 +++++
>>   drivers/iommu/iommu-sva-lib.c | 58 +++++++++++++++++++++++++++++++++++
>>   drivers/iommu/iommu.c         |  4 +++
>>   5 files changed, 80 insertions(+)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index ae0cfca064e6..47610f21d451 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -105,6 +105,9 @@ struct iommu_domain {
>>   	unsigned long pgsize_bitmap;	/* Bitmap of page sizes in use */
>>   	struct iommu_domain_geometry geometry;
>>   	struct iommu_dma_cookie *iova_cookie;
>> +	enum iommu_page_response_code (*iopf_handler)(struct iommu_fault *fault,
>> +						      void *data);
>> +	void *fault_data;
>>   	union {
>>   		struct {
>>   			iommu_fault_handler_t handler;
> 
> Why do we need two falut callbacks? The only difference is that one is
> recoverable and the other is not, right?
> 
> Can we run both down the same op?

The iommu_fault_handler_t is for report_iommu_fault() which could be
replaced with the newer iommu_report_device_fault().

https://lore.kernel.org/linux-iommu/Yo4Nw9QyllT1RZbd@myrica/

> 
>> +/*
>> + * I/O page fault handler for SVA
>> + */
>> +enum iommu_page_response_code
>> +iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
>> +{
>> +	vm_fault_t ret;
>> +	struct vm_area_struct *vma;
>> +	struct mm_struct *mm = data;
>> +	unsigned int access_flags = 0;
>> +	unsigned int fault_flags = FAULT_FLAG_REMOTE;
>> +	struct iommu_fault_page_request *prm = &fault->prm;
>> +	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
>> +
>> +	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
>> +		return status;
>> +
>> +	if (IS_ERR_OR_NULL(mm) || !mmget_not_zero(mm))
> 
> Do not use IS_ERR_ON_NULL. mm should never be null here since the
> fault handler should have been removed from the domain before the
> fault_data is changed.

Yes. Updated.

Best regards,
baolu