Re: [PATCH v10 09/41] KVM: guest_memfd: Filter both shared and private when invalidating

[Fuad Tabba]

On Fri, 7 Aug 2026 at 23:52, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> Before conversion, a guest_memfd could be either all shared, or all
> private, configured at creation time using the INIT_SHARED flag. Hence,
> when zapping pages from stage 2 page tables, guest_memfd can filter which
> to zap based on the initial shared/private state.
>
> With conversion, guest_memfd tracks shared/private state on a per-page
> level, so a range can contain both private and shared pages. Zap both
> private and shared pages for simplicity.
>
> An alternative would be to iterate guest_memfd attributes and only zap both
> if shared and private pages exist within the range. Setting both the shared
> and private filters lets the zapping logic do that iteration instead.
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>

Cheers,
/fuad

> ---
>  virt/kvm/guest_memfd.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 75979c885e030..b1537226e5adf 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -136,14 +136,6 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
>         return folio;
>  }
>
> -static enum kvm_gfn_range_filter kvm_gmem_get_invalidate_filter(struct inode *inode)
> -{
> -       if (GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED)
> -               return KVM_FILTER_SHARED;
> -
> -       return KVM_FILTER_PRIVATE;
> -}
> -
>  static void __kvm_gmem_invalidate_start(struct gmem_file *f, pgoff_t start,
>                                         pgoff_t end,
>                                         enum kvm_gfn_range_filter attr_filter)
> @@ -186,15 +178,13 @@ static void __kvm_gmem_invalidate_start(struct gmem_file *f, pgoff_t start,
>  }
>
>  static void kvm_gmem_invalidate_start(struct inode *inode, pgoff_t start,
> -                                     pgoff_t end)
> +                                     pgoff_t end,
> +                                     enum kvm_gfn_range_filter filter)
>  {
> -       enum kvm_gfn_range_filter attr_filter;
>         struct gmem_file *f;
>
> -       attr_filter = kvm_gmem_get_invalidate_filter(inode);
> -
>         kvm_gmem_for_each_file(f, inode)
> -               __kvm_gmem_invalidate_start(f, start, end, attr_filter);
> +               __kvm_gmem_invalidate_start(f, start, end, filter);
>  }
>
>  static void __kvm_gmem_invalidate_end(struct gmem_file *f, pgoff_t start,
> @@ -229,7 +219,8 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>          */
>         filemap_invalidate_lock(inode->i_mapping);
>
> -       kvm_gmem_invalidate_start(inode, start, end);
> +       kvm_gmem_invalidate_start(inode, start, end,
> +                                 KVM_FILTER_SHARED | KVM_FILTER_PRIVATE);
>
>         truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1);
>
> @@ -344,7 +335,7 @@ static int kvm_gmem_release(struct inode *inode, struct file *file)
>          * memory, as its lifetime is associated with the inode, not the file.
>          */
>         __kvm_gmem_invalidate_start(f, 0, -1ul,
> -                                   kvm_gmem_get_invalidate_filter(inode));
> +                                   KVM_FILTER_SHARED | KVM_FILTER_PRIVATE);
>         __kvm_gmem_invalidate_end(f, 0, -1ul);
>
>         list_del(&f->entry);
> @@ -525,7 +516,8 @@ static int kvm_gmem_error_folio(struct address_space *mapping, struct folio *fol
>         start = folio->index;
>         end = start + folio_nr_pages(folio);
>
> -       kvm_gmem_invalidate_start(mapping->host, start, end);
> +       kvm_gmem_invalidate_start(mapping->host, start, end,
> +                                 KVM_FILTER_SHARED | KVM_FILTER_PRIVATE);
>
>         /*
>          * Do not truncate the range, what action is taken in response to the
>
> --
> 2.55.0.654.g21b8a5bc05-goog
>
>