Re: [PATCH v10 13/41] KVM: guest_memfd: Return early if range already has requested attributes

On 8/8/2026 5:52 AM, Ackerley Tng via B4 Relay wrote:
> From: Ackerley Tng <[email protected]>
> 
> Provide function to check that a range has given attributes.
> 
> Optimize setting memory attributes by returning early if all pages in the
> requested range already has the requested attributes.
> 
> Reviewed-by: Fuad Tabba <[email protected]>
> Tested-by: Shivank Garg <[email protected]>
> Signed-off-by: Ackerley Tng <[email protected]>

Reviewed-by: Xiaoyao Li <[email protected]>

> ---
>   virt/kvm/guest_memfd.c | 23 ++++++++++++++++++++++-
>   1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index c9874bd85c5d8..896699afcad9d 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -95,6 +95,24 @@ static bool kvm_gmem_is_shared_mem(struct inode *inode, pgoff_t index)
>   	return !kvm_gmem_is_private_mem(inode, index);
>   }
>   
> +static bool kvm_gmem_range_has_attributes(struct inode *inode,
> +					  pgoff_t index, size_t nr_pages,
> +					  u64 attributes)
> +{
> +	struct maple_tree *mt = &GMEM_I(inode)->attributes;
> +	pgoff_t end = index + nr_pages - 1;
> +	void *entry;
> +
> +	lockdep_assert(mt_lock_is_held(mt));
> +
> +	mt_for_each(mt, entry, index, end) {
> +		if (kvm_gmem_get_attributes(inode, entry) != attributes)
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
>   /*
>    * Returns a locked folio on success.  The caller is responsible for
>    * setting the up-to-date flag before the memory is mapped into the guest.
> @@ -605,12 +623,15 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>   	pgoff_t end = start + nr_pages;
>   	struct maple_tree *mt;
>   	struct ma_state mas;
> -	int r;
> +	int r = 0;
>   
>   	mt = &gi->attributes;
>   
>   	filemap_invalidate_lock(mapping);
>   
> +	if (kvm_gmem_range_has_attributes(inode, start, nr_pages, attrs))
> +		goto out;
> +
>   	mas_init(&mas, mt, start);
>   	r = kvm_gmem_mas_preallocate(&mas, attrs, start, nr_pages);
>   	if (r) {
>