Re: [PATCH v2 08/20] KVM: s390: KVM page table management functions: allocation

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Sep 10, 2025 at 08:07:34PM +0200, Claudio Imbrenda wrote:
> Add page table management functions to be used for KVM guest (gmap)
> page tables.
> 
> This patch adds the boilerplate and functions for the allocation and
> deallocation of DAT tables.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>  arch/s390/kvm/Makefile     |  1 +
>  arch/s390/kvm/dat.c        | 91 ++++++++++++++++++++++++++++++++++++++
>  arch/s390/kvm/dat.h        |  4 ++
>  arch/s390/mm/page-states.c |  1 +
>  4 files changed, 97 insertions(+)
>  create mode 100644 arch/s390/kvm/dat.c

...

> +static inline struct page_table *dat_alloc_pt_noinit(void)
> +{
> +	struct page *page;
> +	void *virt;
> +
> +	page = alloc_pages(GFP_ATOMIC, 0);
> +	if (!page)
> +		return NULL;
> +
> +	virt = page_to_virt(page);
> +	__arch_set_page_dat(virt, 1);
> +	return virt;
> +}

Is GFP_ATOMIC a typo, and this should have been GFP_KERNEL?

Otherwise I would guess this will cause problems in the future when
under memory pressure allocating guest page tables fails easily,
while before this change such allocations never failed.