Re: [PATCH v4 21/24] s390/uv: Rename find_secret() to uv_find_secret() and publish

[Steffen Eiden <seiden@linux.ibm.com>]

On Wed, Apr 09, 2025 at 04:03:02PM +0200, Harald Freudenberger wrote:
> Rename the internal UV function find_secret() to uv_find_secret()
> and publish it as new UV API in-kernel function.
> 
> The pkey uv handler may be called in a do-not-allocate memory
> situation where sleeping is allowed but allocating memory which
> may cause IO operations is not. For example when an encrypted
> swap file is used and the encryption is done via UV retrievable
> secrets with protected keys.
> 
> The UV API function uv_get_secret_metadata() allocates memory
> and then calls the find_secret() function. By exposing the
> find_secret() function as a new UV API function uv_find_secret()
> it is possible to retrieve UV secret meta data without any
> memory allocations from the UV when the caller offers space
> for one struct uv_secret_list.
> 
> Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>

With the documentation improved:

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>

> ---
>  arch/s390/include/asm/uv.h |  3 +++
>  arch/s390/kernel/uv.c      | 12 ++++++++----
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index b11f5b6d0bd1..8d7e00fa2bf0 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -616,6 +616,9 @@ static inline int uv_remove_shared(unsigned long addr)
>  	return share(addr, UVC_CMD_REMOVE_SHARED_ACCESS);
>  }
>  
> +int uv_find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
> +		   struct uv_secret_list *list,
> +		   struct uv_secret_list_item_hdr *secret);
>  int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
>  			   struct uv_secret_list_item_hdr *secret);
>  int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size);
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index 9f05df2da2f7..4acbbdff568f 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -681,12 +681,15 @@ static int find_secret_in_page(const u8 secret_id[UV_SECRET_ID_LEN],
>  
>  /*
This documentation string does not make sense for an exported function. Let's
add documentation from the get_metadata function.

>   * Do the actual search for `uv_get_secret_metadata`.
Change this to something like:

Locate a secret in the list by its id.

> + * @secret_id: search pattern.
> + * @list: ephemeral buffer space
> + * @secret: output data, containing the secret's metadata.
>   *
Add:
    * Search for a secret with the given secret_id in the Ultravisor secret store.

>   * Context: might sleep.
>   */
> -static int find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
> -		       struct uv_secret_list *list,
> -		       struct uv_secret_list_item_hdr *secret)
> +int uv_find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
> +		   struct uv_secret_list *list,
> +		   struct uv_secret_list_item_hdr *secret)

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