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;
> }
> }
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
duplicate insertions and all the nasty lock gymnastics that go along
with it. I'd rather we just support huge_fault. Thanks,
Alex
