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

[Ethan Zhao]

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@xxxxxxxxxxxxxxx>
> > > Reviewed-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > > ---
> > >   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 ? :)


Thanks，

Ethan

> 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))
--
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