Re: [PATCH v6 17/43] KVM: guest_memfd: Determine invalidation filter from memory attributes

[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>
>
> Before conversion, the range filter doesn't really matter:
>
> + For non-CoCo VMs that use guest_memfd, they have no mirrored tdp, so
>   KVM_DIRECT_ROOTS would have been invalidated anyway.
> + CoCo VMs could not use INIT_SHARED, and there's no conversion support, so
>   always using KVM_FILTER_PRIVATE would have worked.
>
> Now with conversion support, update kvm_gmem_get_invalidate_filter to
> inspect the memory attributes maple tree for a given range.
>
> Instead of determining the invalidation filter based on static inode
> flags, iterate through the attributes maple tree for the specific range
> being invalidated. This allows KVM to identify if the range contains
> private pages, shared pages, or both, and set the filter bits
> accordingly.
>
> Update kvm_gmem_invalidate_begin and kvm_gmem_release to pass the range
> parameters to the filter helper to ensure invalidation accurately
> targets the memory types present in the affected range.
>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad
> ---
>  virt/kvm/guest_memfd.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 9f6eebfb68f6b..c9f155c2dc5c5 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -193,12 +193,24 @@ 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)
> +static enum kvm_gfn_range_filter kvm_gmem_get_invalidate_filter(
> +               struct inode *inode, pgoff_t start, pgoff_t end)
>  {
> -       if (GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED)
> -               return KVM_FILTER_SHARED;
> +       struct gmem_inode *gi = GMEM_I(inode);
> +       enum kvm_gfn_range_filter filter = 0;
> +       void *entry;
> +
> +       lockdep_assert(mt_lock_is_held(&gi->attributes));
> +
> +       mt_for_each(&gi->attributes, entry, start, end - 1) {
> +               filter |= (xa_to_value(entry) & KVM_MEMORY_ATTRIBUTE_PRIVATE) ?
> +                         KVM_FILTER_PRIVATE : KVM_FILTER_SHARED;
> +
> +               if (filter == (KVM_FILTER_PRIVATE | KVM_FILTER_SHARED))
> +                       break;
> +       }
>
> -       return KVM_FILTER_PRIVATE;
> +       return filter;
>  }
>
>  static void __kvm_gmem_invalidate_begin(struct gmem_file *f, pgoff_t start,
> @@ -244,7 +256,7 @@ static void kvm_gmem_invalidate_begin(struct inode *inode, pgoff_t start,
>         enum kvm_gfn_range_filter attr_filter;
>         struct gmem_file *f;
>
> -       attr_filter = kvm_gmem_get_invalidate_filter(inode);
> +       attr_filter = kvm_gmem_get_invalidate_filter(inode, start, end);
>
>         kvm_gmem_for_each_file(f, inode)
>                 __kvm_gmem_invalidate_begin(f, start, end, attr_filter);
> @@ -367,6 +379,7 @@ static long kvm_gmem_fallocate(struct file *file, int mode, loff_t offset,
>  static int kvm_gmem_release(struct inode *inode, struct file *file)
>  {
>         struct gmem_file *f = file->private_data;
> +       enum kvm_gfn_range_filter filter;
>         struct kvm_memory_slot *slot;
>         struct kvm *kvm = f->kvm;
>         unsigned long index;
> @@ -398,8 +411,8 @@ static int kvm_gmem_release(struct inode *inode, struct file *file)
>          * memory, as its lifetime is associated with the inode, not the file.
>          */
>         end = i_size_read(inode) >> PAGE_SHIFT;
> -       __kvm_gmem_invalidate_begin(f, 0, end,
> -                                   kvm_gmem_get_invalidate_filter(inode));
> +       filter = kvm_gmem_get_invalidate_filter(inode, 0, end);
> +       __kvm_gmem_invalidate_begin(f, 0, end, filter);
>         __kvm_gmem_invalidate_end(f, 0, end);
>
>         list_del(&f->entry);
>
> --
> 2.54.0.563.g4f69b47b94-goog
>
>