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

[Claudio Imbrenda]

On Wed, 02 Sep 2026 09:15:12 +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.

I have some objections to this series, but not because of what you are
trying to do (which is actually nice).

I understand that you probably wanted to touch as little code as
possible, but now since you're rewriting the allocations to use
kmalloc.... I'd like them to be converted to use the __free(kvmalloc)
system. It will make the code smaller, easier to read and understand,
less prone to future errors, etc.

In some places the whole code flow can be simplified a lot.
 
> 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/
> 
> ---
> 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 |  9 +++++----
>  arch/s390/kvm/s390/interrupt.c |  8 ++++----
>  arch/s390/kvm/s390/priv.c      | 19 ++++++++++---------
>  arch/s390/kvm/s390/s390.c      | 12 ++++++------
>  4 files changed, 25 insertions(+), 23 deletions(-)
> ---
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> change-id: 20260828-s390-kvm-2015b0d777dc
> 
> --
> Sincerely yours,
> Mike.
>