Re: [PATCH 0/3] s390: Diag204 Rework

[Mete Durlu <meted@linux.ibm.com>]

On 21/10/2026 12:28, Mete Durlu wrote:

[...snip...]

> Considerations
> ========================================================================
> * At the moment diag204 size request returns a page count requirement of
>    423. That is the maximum amount of space needed currently for a CEC to
>    service diag204.
>    With this series at times there will be ~6Mb (1.6Mb for each; cache,
>    temp, user buffer...) memory allocated for diag204 data per lpar.
> 
> * With the new IOCTL interface, userspace is defaulted to the
>    largest diag204 data request subcode available(from subcodes 4, 6 and
>    7 always the largest available is used as it returns more data).
>    While this aligns with the existing behavior, question is, would
>    there be any value in allowing users to specify which subcode to use?
>    Although this also means more complicated implementation.
> 
> * A new addition with the IOCTL interface are the allow_busy and
>    allow_busy_wait toggles. For sure there is benefit in allowing diag204
>    to return BUSY instead of waiting for longer durations when it is not
>    ready at the moment. allow_busy_wait adds an interruptable polling
>    loop around that, with that mechanism diag204 users from userspace can
>    wait for diag204 to return from its BUSY state within the same system
>    call. Obviously using only a single system call is better but diag204
>    users are not performance critical atm and the same polling can be
>    implemented from userspace side. This can help reduce some complexity
>    on the kernel code.
> 
> Changes from the earlier series;
> * Address mutex lockdep issues (Sumanth Korikkar)
> * Add permission check for IOCTL (Sumanth Korikkar)
> * Pass buffers set to 0 when calling diag (Sumanth Korikkar)
> 
> ---
> base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
> 
> Mete Durlu (3):
>        s390/diag204: Introduce diag204 rework
>        s390/diag204: Replace diag204 users with new implementation
>        s390/diag: Add diag204 IOCTL to diag misc device
> 
>   arch/s390/hypfs/hypfs_diag.c       | 140 ++------------
>   arch/s390/hypfs/hypfs_diag.h       |   4 +-
>   arch/s390/hypfs/hypfs_diag_fs.c    |   9 +-
>   arch/s390/include/asm/diag.h       |   8 +-
>   arch/s390/include/uapi/asm/diag.h  |   8 +
>   arch/s390/kernel/diag/Makefile     |   2 +-
>   arch/s390/kernel/diag/diag204.c    | 382 +++++++++++++++++++++++++++++++++++++
>   arch/s390/kernel/diag/diag_ioctl.h |   3 +
>   arch/s390/kernel/diag/diag_misc.c  |  10 +
>   arch/s390/kernel/sthyi.c           |  28 +--
>   10 files changed, 437 insertions(+), 157 deletions(-)

I will submit a new version soon with Sashiko findings addressed.
I kindly ask to hold any comments until then.

Thank you!