Re: [PATCH v9 10/11] iommu: Per-domain I/O page fault handling

[Baolu Lu <baolu.lu@linux.intel.com>]

Hi Ethan,

On 2022/6/27 21:03, Ethan Zhao wrote:
> Hi,
> 
> 在 2022/6/21 22:43, Lu Baolu 写道:
>> Tweak the I/O page fault handling framework to route the page faults to
>> the domain and call the page fault handler retrieved from the domain.
>> This makes the I/O page fault handling framework possible to serve more
>> usage scenarios as long as they have an IOMMU domain and install a page
>> fault handler in it. Some unused functions are also removed to avoid
>> dead code.
>>
>> The iommu_get_domain_for_dev_pasid() which retrieves attached domain
>> for a {device, PASID} pair is used. It will be used by the page fault
>> handling framework which knows {device, PASID} reported from the iommu
>> driver. We have a guarantee that the SVA domain doesn't go away during
>> IOPF handling, because unbind() waits for pending faults with
>> iopf_queue_flush_dev() before freeing the domain. Hence, there's no need
>> to synchronize life cycle of the iommu domains between the unbind() and
>> the interrupt threads.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
>> ---
>>   drivers/iommu/io-pgfault.c | 64 +++++---------------------------------
>>   1 file changed, 7 insertions(+), 57 deletions(-)
>>
>> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
>> index aee9e033012f..4f24ec703479 100644
>> --- a/drivers/iommu/io-pgfault.c
>> +++ b/drivers/iommu/io-pgfault.c
>> @@ -69,69 +69,18 @@ static int iopf_complete_group(struct device *dev, 
>> struct iopf_fault *iopf,
>>       return iommu_page_response(dev, &resp);
>>   }
>> -static enum iommu_page_response_code
>> -iopf_handle_single(struct iopf_fault *iopf)
>> -{
>> -    vm_fault_t ret;
>> -    struct mm_struct *mm;
>> -    struct vm_area_struct *vma;
>> -    unsigned int access_flags = 0;
>> -    unsigned int fault_flags = FAULT_FLAG_REMOTE;
>> -    struct iommu_fault_page_request *prm = &iopf->fault.prm;
>> -    enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
>> -
>> -    if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
>> -        return status;
>> -
>> -    mm = iommu_sva_find(prm->pasid);
>> -    if (IS_ERR_OR_NULL(mm))
>> -        return status;
>> -
>> -    mmap_read_lock(mm);
>> -
>> -    vma = find_extend_vma(mm, prm->addr);
>> -    if (!vma)
>> -        /* Unmapped area */
>> -        goto out_put_mm;
>> -
>> -    if (prm->perm & IOMMU_FAULT_PERM_READ)
>> -        access_flags |= VM_READ;
>> -
>> -    if (prm->perm & IOMMU_FAULT_PERM_WRITE) {
>> -        access_flags |= VM_WRITE;
>> -        fault_flags |= FAULT_FLAG_WRITE;
>> -    }
>> -
>> -    if (prm->perm & IOMMU_FAULT_PERM_EXEC) {
>> -        access_flags |= VM_EXEC;
>> -        fault_flags |= FAULT_FLAG_INSTRUCTION;
>> -    }
>> -
>> -    if (!(prm->perm & IOMMU_FAULT_PERM_PRIV))
>> -        fault_flags |= FAULT_FLAG_USER;
>> -
>> -    if (access_flags & ~vma->vm_flags)
>> -        /* Access fault */
>> -        goto out_put_mm;
>> -
>> -    ret = handle_mm_fault(vma, prm->addr, fault_flags, NULL);
>> -    status = ret & VM_FAULT_ERROR ? IOMMU_PAGE_RESP_INVALID :
>> -        IOMMU_PAGE_RESP_SUCCESS;
>> -
>> -out_put_mm:
>> -    mmap_read_unlock(mm);
>> -    mmput(mm);
>> -
>> -    return status;
>> -}
>> -
> 
> Once the iopf_handle_single() is removed, the name of 
> iopf_handle_group() looks a little weired
> 
> and confused, does this group mean the iommu group (domain) ? while I 
> take some minutes to

No. This is not the iommu group. It's page request group defined by the
PCI SIG spec. Multiple page requests could be put in a group with a
same group id. All page requests in a group could be responded to device
in one shot.

Best regards,
baolu

> 
> look into the code, oh, means a batch / list / queue  of iopfs , and 
> iopf_handle_group() becomes a
> 
> generic iopf_handler() .
> 
> Doe it make sense to revise the names of iopf_handle_group(), 
> iopf_complete_group,  iopf_group in
> 
> this patch set ?
> 
> 
> Thanks,
> 
> Ethan
> 
>>   static void iopf_handle_group(struct work_struct *work)
>>   {
>>       struct iopf_group *group;
>> +    struct iommu_domain *domain;
>>       struct iopf_fault *iopf, *next;
>>       enum iommu_page_response_code status = IOMMU_PAGE_RESP_SUCCESS;
>>       group = container_of(work, struct iopf_group, work);
>> +    domain = iommu_get_domain_for_dev_pasid(group->dev,
>> +                group->last_fault.fault.prm.pasid);
>> +    if (!domain || !domain->iopf_handler)
>> +        status = IOMMU_PAGE_RESP_INVALID;
>>       list_for_each_entry_safe(iopf, next, &group->faults, list) {
>>           /*
>> @@ -139,7 +88,8 @@ static void iopf_handle_group(struct work_struct 
>> *work)
>>            * faults in the group if there is an error.
>>            */
>>           if (status == IOMMU_PAGE_RESP_SUCCESS)
>> -            status = iopf_handle_single(iopf);
>> +            status = domain->iopf_handler(&iopf->fault,
>> +                              domain->fault_data);
>>           if (!(iopf->fault.prm.flags &
>>                 IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
>