Re: [PATCH 01/33] s390: Use _pt_s390_gaddr for gmap address tracking

[David Hildenbrand <david@xxxxxxxxxx>]

On 17.04.23 22:50, Vishal Moola (Oracle) wrote:
> s390 uses page->index to keep track of page tables for the guest address
> space. In an attempt to consolidate the usage of page fields in s390,
> replace _pt_pad_2 with _pt_s390_gaddr to replace page->index in gmap.
>
> This will help with the splitting of struct ptdesc from struct page, as
> well as allow s390 to use _pt_frag_refcount for fragmented page table
> tracking.
>
> Since page->_pt_s390_gaddr aliases with mapping, ensure its set to NULL
> before freeing the pages as well.
>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
> ---
[...]

> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 3fc9e680f174..2616d64c0e8c 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -144,7 +144,7 @@ struct page {
>                 struct {        /* Page table pages */
>                         unsigned long _pt_pad_1;        /* compound_head */
>                         pgtable_t pmd_huge_pte; /* protected by page->ptl */
> -                       unsigned long _pt_pad_2;        /* mapping */
> +                       unsigned long _pt_s390_gaddr;   /* mapping */
>                         union {
>                                 struct mm_struct *pt_mm; /* x86 pgds only */
>                                 atomic_t pt_frag_refcount; /* powerpc */
The confusing part is, that these gmap page tables are not ordinary 
process page tables that we would ordinarily place into this section 
here. That's why they are also not allocated/freed using the typical 
page table constructor/destructor ...
--
Thanks,

David / dhildenb