Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic

Lu Baolu
2022-03-22T05:28:49Z

On 2022/3/21 19:39, Jean-Philippe Brucker wrote:
> On Sun, Mar 20, 2022 at 02:40:29PM +0800, Lu Baolu wrote:
>> The existing IOPF handling framework only handles the I/O page faults for
>> SVA. Ginven that we are able to link iommu domain with each I/O page fault,
>> we can now make the I/O page fault handling framework more general for
>> more types of page faults.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> include/linux/iommu.h | 4 +++
>> drivers/iommu/io-pgfault.c | 67 ++++++-----------------------------
>> drivers/iommu/iommu-sva-lib.c | 59 ++++++++++++++++++++++++++++++
>> 3 files changed, 73 insertions(+), 57 deletions(-)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 803e7b07605e..11c65a7bed88 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -50,6 +50,8 @@ struct iommu_dma_cookie;
>> typedef int (*iommu_fault_handler_t)(struct iommu_domain *,
>> struct device *, unsigned long, int, void *);
>> typedef int (*iommu_dev_fault_handler_t)(struct iommu_fault *, void *);
>> +typedef enum iommu_page_response_code (*iommu_domain_iopf_handler_t)
>> + (struct iommu_fault *, void *);
>>
>> struct iommu_domain_geometry {
>> dma_addr_t aperture_start; /* First address that can be mapped */
>> @@ -101,6 +103,8 @@ struct iommu_domain {
>> struct iommu_domain_geometry geometry;
>> struct iommu_dma_cookie *iova_cookie;
>> struct mm_struct *sva_cookie;
>> + iommu_domain_iopf_handler_t fault_handler;
>> + void *fault_data;
>> };
>>
>> static inline bool iommu_is_dma_domain(struct iommu_domain *domain)
>> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
>> index 1df8c1dcae77..dad0e40cd8d2 100644
>> --- a/drivers/iommu/io-pgfault.c
>> +++ b/drivers/iommu/io-pgfault.c
>> @@ -69,62 +69,6 @@ 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;
>> -}
>> -
>> static void iopf_handle_group(struct work_struct *work)
>> {
>> struct iopf_group *group;
>> @@ -134,12 +78,21 @@ static void iopf_handle_group(struct work_struct *work)
>> group = container_of(work, struct iopf_group, work);
>>
>> list_for_each_entry_safe(iopf, next, &group->faults, list) {
>> + struct iommu_domain *domain;
>> +
>> + domain = iommu_get_domain_for_dev_pasid(group->dev,
>> + iopf->fault.prm.pasid);
>
> Do we have a guarantee that the domain is not freed while we handle the
> fault? We could prevent unbind() while there are pending faults on this
> bond. But a refcount on SVA domains could defer freeing, and would also
> help with keeping the semantics where bind() returns a single refcounted
> bond for any {dev, mm}.
>
> Given that this path is full of circular locking pitfalls, and to keep the
> fault handler efficient (well, at least not make it worse), we should
> probably keep a getter like iommu_sva_find() that does not require
> locking.

Agreed. We need a mechanism to ensure concurrency. I will look into it.

>
>> +
>> + if (!domain || !domain->fault_handler)
>> + status = IOMMU_PAGE_RESP_INVALID;
>> +
>> /*
>> * For the moment, errors are sticky: don't handle subsequent
>> * faults in the group if there is an error.
>> */
>> if (status == IOMMU_PAGE_RESP_SUCCESS)
>> - status = iopf_handle_single(iopf);
>> + status = domain->fault_handler(&iopf->fault,
>> + domain->fault_data);
>
> If we make this a direct call and only use a light getter for the
> PASID->mm lookup we don't need to look at the domain at all. Or are you
> planning to add external fault handlers?

Yes. I'd like the I/O page fault handling framework to work for
external domains as well, for example, the I/O page faults for user
space page table should be routed to user space.

>
>>
>> if (!(iopf->fault.prm.flags &
>> IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
>> diff --git a/drivers/iommu/iommu-sva-lib.c b/drivers/iommu/iommu-sva-lib.c
>> index 47cf98e661ff..01fa8096bd02 100644
>> --- a/drivers/iommu/iommu-sva-lib.c
>> +++ b/drivers/iommu/iommu-sva-lib.c
>> @@ -87,6 +87,63 @@ static struct iommu_domain *iommu_sva_domain_alloc(struct device *dev)
>> return domain;
>> }
>>
>> +static enum iommu_page_response_code
>> +iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
>> +{
>> + vm_fault_t ret;
>> + struct mm_struct *mm;
>> + struct vm_area_struct *vma;
>> + unsigned int access_flags = 0;
>> + struct iommu_domain *domain = data;
>> + 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;
>> +
>> + mm = domain->sva_cookie;
>> + 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);
>
> mmget_not_zero() is missing since iommu_sva_find() is gone. I'm guessing
> we still need it in case the process dies

Agreed.

>
> Thanks,
> Jean

Best regards,
baolu