Re: [PATCH v6 12/43] KVM: guest_memfd: Call arch invalidate hooks on conversion

[Fuad Tabba]

On Thu, 7 May 2026 at 21:22, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> When memory in guest_memfd is converted from private to shared, the
> platform-specific state associated with the guest-private pages must be
> invalidated or cleaned up.
>
> Iterate over the folios in the affected range and call the
> kvm_arch_gmem_invalidate() hook for each PFN range. This allows
> architectures to perform necessary teardown, such as updating hardware
> metadata or encryption states, before the pages are transitioned to the
> shared state.
>
> Invoke this helper after indicating to KVM's mmu code that an invalidation
> is in progress to stop in-flight page faults from succeeding.
>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Minor nit below, but lgtm.

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

> ---
>  virt/kvm/guest_memfd.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 9d82642a025e9..baf4b88dead1f 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -603,6 +603,42 @@ static bool kvm_gmem_is_safe_for_conversion(struct inode *inode, pgoff_t start,
>         return safe;
>  }
>
> +#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
> +static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end)
> +{
> +       struct folio_batch fbatch;
> +       pgoff_t next = start;
> +       int i;
> +
> +       folio_batch_init(&fbatch);
> +       while (filemap_get_folios(inode->i_mapping, &next, end - 1, &fbatch)) {
> +               for (i = 0; i < folio_batch_count(&fbatch); ++i) {
> +                       struct folio *folio = fbatch.folios[i];
> +                       pgoff_t start_index, end_index;
> +                       kvm_pfn_t start_pfn, end_pfn;
> +
> +                       start_index = max(start, folio->index);
> +                       end_index = min(end, folio_next_index(folio));
> +                       /*
> +                        * end_index is either in folio or points to
> +                        * the first page of the next folio. Hence,
> +                        * all pages in range [start_index, end_index)
> +                        * are contiguous.
> +                        */
> +                       start_pfn = folio_file_pfn(folio, start_index);
> +                       end_pfn = start_pfn + end_index - start_index;
> +
> +                       kvm_arch_gmem_invalidate(start_pfn, end_pfn);
> +               }
> +
> +               folio_batch_release(&fbatch);
> +               cond_resched();
> +       }
> +}
> +#else
> +static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end) {}
> +#endif
> +
>  static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>                                      size_t nr_pages, uint64_t attrs,
>                                      pgoff_t *err_index)
> @@ -643,7 +679,12 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>          */
>
>         kvm_gmem_invalidate_begin(inode, start, end);
> +
> +       if (!to_private)
> +               kvm_gmem_invalidate(inode, start, end);
> +
>         mas_store_prealloc(&mas, xa_mk_value(attrs));
> +

Why the unrelated extra space?

>         kvm_gmem_invalidate_end(inode, start, end);
>  out:
>         filemap_invalidate_unlock(mapping);
>
> --
> 2.54.0.563.g4f69b47b94-goog
>
>