linux-kernel - Re: [PATCH] sparc64: fix hugetlb for sun4u

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Message-ID: <b7ad6ad9-c1ed-4a53-a73e-4a4306107a55@gaisler.com>
Date: Fri, 19 Sep 2025 20:01:00 +0200
From: Andreas Larsson <andreas@...sler.com>
To: Anthony Yznaga <anthony.yznaga@...cle.com>, sparclinux@...r.kernel.org,
 davem@...emloft.net
Cc: linux-kernel@...r.kernel.org, agordeev@...ux.ibm.com, will@...nel.org,
 ryan.roberts@....com, david@...hat.com, osalvador@...e.de
Subject: Re: [PATCH] sparc64: fix hugetlb for sun4u

On 2025-07-16 03:24, 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@...r.kernel.org
> Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
> ---
>  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: Andreas Larsson <andreas@...sler.com>

Picking this up to my for-next.

Thanks,
Andreas