Re: [PATCH] sparc64: fix hugetlb for sun4u

[John Paul Adrian Glaubitz]

Hi Anthony,

On Tue, 2025-07-15 at 18:24 -0700, Anthony Yznaga wrote:
> An attempt to exercise sparc hugetlb code in a sun4u-based guest
> running under qemu results in the guest hanging due to being stuck
> in a trap loop. This is due to invalid hugetlb TTEs being installed
> that do not have the expected _PAGE_PMD_HUGE and page size bits set.
> Although the breakage has gone apparently unnoticed for several years,
> fix it now so there is the option to exercise sparc hugetlb code under
> qemu. This can be useful because sun4v support in qemu does not support
> linux guests currently and sun4v-based hardware resources may not be
> readily available.
> 
> Fix tested with a 6.15.2 and 6.16-rc6 kernels by running libhugetlbfs
> tests on a qemu guest running Debian 13.
> 
> Fixes: c7d9f77d33a7 ("sparc64: Multi-page size support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx>
> ---
>  arch/sparc/mm/hugetlbpage.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/sparc/mm/hugetlbpage.c b/arch/sparc/mm/hugetlbpage.c
> index 80504148d8a5..2048b5c42ca8 100644
> --- a/arch/sparc/mm/hugetlbpage.c
> +++ b/arch/sparc/mm/hugetlbpage.c
> @@ -22,6 +22,26 @@
>  
>  static pte_t sun4u_hugepage_shift_to_tte(pte_t entry, unsigned int shift)
>  {
> +	unsigned long hugepage_size = _PAGE_SZ4MB_4U;
> +
> +	pte_val(entry) = pte_val(entry) & ~_PAGE_SZALL_4U;
> +
> +	switch (shift) {
> +	case HPAGE_256MB_SHIFT:
> +		hugepage_size = _PAGE_SZ256MB_4U;
> +		pte_val(entry) |= _PAGE_PMD_HUGE;
> +		break;
> +	case HPAGE_SHIFT:
> +		pte_val(entry) |= _PAGE_PMD_HUGE;
> +		break;
> +	case HPAGE_64K_SHIFT:
> +		hugepage_size = _PAGE_SZ64K_4U;
> +		break;
> +	default:
> +		WARN_ONCE(1, "unsupported hugepage shift=%u\n", shift);
> +	}
> +
> +	pte_val(entry) = pte_val(entry) | hugepage_size;
>  	return entry;
>  }
>  

Reviewed-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>

Thanks,
Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913