On Fri, May 31, 2024 at 11:18:15PM -0600, Alex Williamson wrote:
> On Sat, 1 Jun 2024 07:41:27 +0800
> Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote:
>
> > On Wed, May 29, 2024 at 10:52:31PM -0600, Alex Williamson wrote:
> > > With the vfio device fd tied to the address space of the pseudo fs
> > > inode, we can use the mm to track all vmas that might be mmap'ing
> > > device BARs, which removes our vma_list and all the complicated lock
> > > ordering necessary to manually zap each related vma.
> > >
> > > Note that we can no longer store the pfn in vm_pgoff if we want to use
> > > unmap_mapping_range() to zap a selective portion of the device fd
> > > corresponding to BAR mappings.
> > >
> > > This also converts our mmap fault handler to use vmf_insert_pfn()
> > > because we no longer have a vma_list to avoid the concurrency problem
> > > with io_remap_pfn_range(). The goal is to eventually use the vm_ops
> > > huge_fault handler to avoid the additional faulting overhead, but
> > > vmf_insert_pfn_{pmd,pud}() need to learn about pfnmaps first.
> > >
> > Do we also consider looped vmf_insert_pfn() in mmap fault handler? e.g.
> > for (i = vma->vm_start; i < vma->vm_end; i += PAGE_SIZE) {
> > offset = (i - vma->vm_start) >> PAGE_SHIFT;
> > ret = vmf_insert_pfn(vma, i, base_pfn + offset);
> > if (ret != VM_FAULT_NOPAGE) {
> > zap_vma_ptes(vma, vma->vm_start, vma->vm_end - vma->vm_start);
> > goto up_out;
> > }
> > }
>
What about the prefault version? e.g.
ret = vmf_insert_pfn(vma, vmf->address, pfn + pgoff);
+ if (ret & VM_FAULT_ERROR)
+ goto out_disabled;
+
+ /* prefault */
+ for (i = vma->vm_start; i < vma->vm_end; i += PAGE_SIZE, pfn++) {
+ if (i == vmf->address)
+ continue;
+
+ /* Don't return error on prefault */
+ if (vmf_insert_pfn(vma, i, pfn) & VM_FAULT_ERROR)
+ break;
+ }
+
out_disabled:
up_read(&vdev->memory_lock);
> We can have concurrent faults, so doing this means that we need to
> continue to maintain a locked list of vmas that have faulted to avoid
But looks vfio_pci_zap_bars() always zap full PCI BAR ranges for vmas in
core_vdev->inode->i_mapping.
So, it doesn't matter whether a vma is fully mapped or partly mapped?
> duplicate insertions and all the nasty lock gymnastics that go along
> with it. I'd rather we just support huge_fault. Thanks,
huge_fault is better. But before that, is this prefault one good?
