Hi David,
On Thu, Feb 22, 2024 at 4:28 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > +static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf)
> > +{
> > + struct folio *folio;
> > +
> > + folio = kvm_gmem_get_folio(file_inode(vmf->vma->vm_file), vmf->pgoff);
> > + if (!folio)
> > + return VM_FAULT_SIGBUS;
> > +
> > + /*
> > + * Check if the page is allowed to be faulted to the host, with the
> > + * folio lock held to ensure that the check and incrementing the page
> > + * count are protected by the same folio lock.
> > + */
> > + if (!kvm_gmem_isfaultable(vmf)) {
> > + folio_unlock(folio);
> > + return VM_FAULT_SIGBUS;
> > + }
> > +
> > + vmf->page = folio_file_page(folio, vmf->pgoff);
>
> We won't currently get hugetlb (or even THP) here. It mimics what shmem
> would do.
At the moment there isn't hugetlb support in guest_memfd(), and
neither in pKVM. Although we do plan on supporting it.
> finish_fault->set_pte_range() will call folio_add_file_rmap_ptes(),
> getting the rmap involved.
>
> Do we have some tests in place that make sure that
> fallocate(FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE) will properly unmap
> the page again (IOW, that the rmap does indeed work?).
I'm not sure if you mean kernel tests, or if I've tested it. There are
guest_memfd() tests for
fallocate(FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE) , which I have
run. I've also tested it manually with sample programs, and it behaves
as expected.
Otherwise, for gunyah Elliot has used folio_mmapped() [], but Matthew
doesn't think that it would do what we'd like it to do, i.e., ensure
that _noone_ can fault in the page [2]
I would appreciate any ideas, comments, or suggestions regarding this.
Thanks!
/fuad
[1] https://lore.kernel.org/all/20240222141602976-0800.eberman@xxxxxxxxxxxxxxxxxxxxxxxxxx/
[2] https://lore.kernel.org/all/ZdfoR3nCEP3HTtm1@xxxxxxxxxxxxxxxxxxxx/
> --
> Cheers,
>
> David / dhildenb
>
