Re: [PATCH v2 0/4] KVM: s390: replace page allocator calls with kzalloc()

[Claudio Imbrenda]

On Sun, 06 Sep 2026 11:27:08 +0300
"Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx> wrote:

> This is a (small) part of larger work of replacing page allocator calls
> with kmalloc.
> 
> My initial intention a few month ago was to remove ugly casts [1], but then
> willy pointed out that Linus objected to something like this [2] and it
> looks like more than a decade old technical debt.
> 
> Largely, anything that doesn't need struct page (or a memdesc in the
> future) should just use kmalloc() or kvmalloc() to allocate memory.
> kmalloc() guarantees alignment, physical contiguity and working
> virt_to_phys() and beside nicer API that returns void * on alloc and
> doesn't require to know the allocation size on free, kmalloc() provides
> better debugging capabilities than page allocator.
> 
> Another thing is that touching these allocation sites gives the reviewers
> opportunity to see if a PAGE_SIZE buffer is actually needed or maybe
> another size is appropriate.
> 
> For larger allocations that don't need physically contiguous memory
> kvmalloc() can be a better option that __get_free_pages() because under
> memory pressure it's is easier to allocate several order-0 pages than a
> physically contiguous chunk with the same number of pages.
> 
> And last, but not least, removing needless calls to page allocator should
> help with memdesc (aka project folio) conversion. There will be way less
> places to audit to see if the user was actually using struct page.
> 
> Also in git:
> https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git gfp-to-kmalloc/s390-kvm
> 
> [1] https://lore.kernel.org/all/20251018093002.3660549-1-rppt@xxxxxxxxxx/
> [2] https://lore.kernel.org/all/CA+55aFwp4iy4rtX2gE2WjBGFL=NxMVnoFeHqYa2j1dYOMMGqxg@xxxxxxxxxxxxxx/
> 

whole series:

Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>

> ---
> v2 changes:
> * Mask out the next CBR entry offset SIE stores in the low bits of cbrlo
>   before handing the address to kfree()
> * Use __free(kfree) in handle_sthyi()
> 
> v1: https://patch.msgid.link/20260902-s390-kvm-v1-0-3bc0986550b1@xxxxxxxxxx
> 
> ---
> Mike Rapoport (Microsoft) (4):
>       KVM: s390: Replace get_zeroed_page() with kzalloc() for the STHYI buffer
>       KVM: s390: Replace get_zeroed_page() with kzalloc() for the STSI buffer
>       KVM: s390: Replace get_zeroed_page() with kzalloc() for the GIB
>       KVM: s390: Replace get_zeroed_page() with kzalloc() for sie_page2 and CMMA
> 
>  arch/s390/kvm/s390/intercept.c | 23 ++++++++++-------------
>  arch/s390/kvm/s390/interrupt.c |  8 ++++----
>  arch/s390/kvm/s390/priv.c      | 19 ++++++++++---------
>  arch/s390/kvm/s390/s390.c      | 12 ++++++------
>  4 files changed, 30 insertions(+), 32 deletions(-)
> ---
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> change-id: 20260828-s390-kvm-2015b0d777dc
> 
> --
> Sincerely yours,
> Mike.
>