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

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Date:   Tue, 28 Jun 2022 19:53:39 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Ethan Zhao <haifeng.zhao@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        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>
Cc:     baolu.lu@...ux.intel.com, Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v9 10/11] iommu: Per-domain I/O page fault handling

On 2022/6/28 17:10, Ethan Zhao wrote:
> Hi, Baolu
> 
> 在 2022/6/28 14:28, Baolu Lu 写道:
>> 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@...ux.intel.com>
>>>> Reviewed-by: Jean-Philippe Brucker <jean-philippe@...aro.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.
> 
> Thanks your explaination, understand the concept of PCIe PRG.  I meant
> 
> do we still have the necessity to mention the "group" here in the name
> 
> iopf_handle_group(),  which one is better ? iopf_handle_prg() or
> 
> iopf_handler(),  perhaps none of them ? :)

Oh! Sorry for the misunderstanding.

I have no strong feeling to change this naming. :-) All the names
express what the helper does. Jean is the author of this framework. If
he has the same idea as you, I don't mind renaming it in this patch.

Best regards,
baolu