Re: [PATCH v4 0/8] s390: Reintroduce support for DCACHE_WORD_ACCESS

[Vasily Gorbik]

On Mon, Jul 20, 2026 at 10:58:26AM +0200, Heiko Carstens wrote:
> v4:
> - Add two more cleanup patches based on Sashiko feedback, however I
>   don't consider them as bug fixes. This is more cosmetics:
>   - Use handle_fault_error() in do_secure_storage_access()
>   - Use goto statement in do_secure_storage_access()
> 
> v3:
> - Fix two more pre-existing bugs reported by Sashiko
> - Add Christian's Tested-by tag to four of the six patches
> 
> v2:
> - Explicitely PAGE_ALIGN size in uv_alloc_stor_var() [Sashiko]
> - Document that lazy PTE update / TLB flushing is intended [Sashiko]
> 
> v1:
> Support for DCACHE_WORD_ACCESS was recently removed [1] since it caused
> problems with the incomplete handling of secure storage access
> exceptions. It looked like fixing the exception handler would be a larger
> effort; therefore support for DCACHE_WORD_ACCESS was removed as a work
> around.
> 
> Address the potential problems that exist with secure storage access
> exceptions and add support for DCACHE_WORD_ACCESS again.
> 
> In particular address the following problems:
> 
> - Reading the guest variable storage area via the /proc/kcore interface
>   results in short reads. Address this by using a VM_SPARSE area for the
>   guest variable storage area. VM_SPARSE areas will be handled like
>   memory holes (zeros will be read).
> 
> - Fix handling of secure storage access exceptions in vmalloc area.
> 
> - Remove folio handling for secure storage access exceptions to avoid
>   potential data corruption.
> 
> [1] 37540b8c287f ("s390: Revert support for DCACHE_WORD_ACCESS")
> 
> Heiko Carstens (8):
>   KVM: s390: pv: Use VM_SPARSE area for guest variable storage area
>   s390/mm: Add missing mm check to do_secure_storage_access()
>   s390/mm: Use lock_mm_and_find_vma() in do_secure_storage_access()
>   s390/mm: Fix handling of vmalloc area in do_secure_storage_access()
>   s390/mm: Remove folio handling for kernel faults in do_secure_storage_access()
>   s390/mm: Use handle_fault_error() in do_secure_storage_access()
>   s390/mm: Use goto statement in do_secure_storage_access()
>   s390: Add support for DCACHE_WORD_ACCESS (again)
> 
>  arch/s390/Kconfig                      |  1 +
>  arch/s390/include/asm/asm-extable.h    |  4 ++
>  arch/s390/include/asm/uv.h             |  2 +
>  arch/s390/include/asm/word-at-a-time.h | 22 +++++++++
>  arch/s390/kernel/uv.c                  | 65 ++++++++++++++++++++++++++
>  arch/s390/kvm/pv.c                     |  6 +--
>  arch/s390/mm/extable.c                 | 18 +++++++
>  arch/s390/mm/fault.c                   | 35 ++++++--------
>  8 files changed, 128 insertions(+), 25 deletions(-)

Applied, thank you!