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

[Baolu Lu]

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@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 ? :)

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