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

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Date:   Mon, 27 Jun 2022 21:03:52 +0800
From:   Ethan Zhao <haifeng.zhao@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...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:     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

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

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))

-- 
"firm, enduring, strong, and long-lived"