Re: [RFC PATCH v2 15/20] powerpc/85xx: Switch to 64 bits PGD

Oscar Salvador
2024-05-25T04:54:54Z

On Fri, May 17, 2024 at 09:00:09PM +0200, Christophe Leroy wrote:
> In order to allow leaf PMD entries, switch the PGD to 64 bits entries.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>

I do not quite understand this change.
Are not powerE500 and power85xx two different things?
You are changing making it 64 for PPC_E500_64bits, but you are updating head_85xx.
Are they sharing this code?

Also, we would benefit from a slightly bigger changelog, explaining why
do we need this change in some more detail.

> diff --git a/arch/powerpc/include/asm/pgtable-types.h b/arch/powerpc/include/asm/pgtable-types.h
> index 082c85cc09b1..db965d98e0ae 100644
> --- a/arch/powerpc/include/asm/pgtable-types.h
> +++ b/arch/powerpc/include/asm/pgtable-types.h
> @@ -49,7 +49,11 @@ static inline unsigned long pud_val(pud_t x)
> #endif /* CONFIG_PPC64 */
>
> /* PGD level */
> +#if defined(CONFIG_PPC_E500) && defined(CONFIG_PTE_64BIT)
> +typedef struct { unsigned long long pgd; } pgd_t;
> +#else
> typedef struct { unsigned long pgd; } pgd_t;
> +#endif
> #define __pgd(x) ((pgd_t) { (x) })
> static inline unsigned long pgd_val(pgd_t x)
> {
> diff --git a/arch/powerpc/kernel/head_85xx.S b/arch/powerpc/kernel/head_85xx.S
> index 39724ff5ae1f..a305244afc9f 100644
> --- a/arch/powerpc/kernel/head_85xx.S
> +++ b/arch/powerpc/kernel/head_85xx.S
> @@ -307,8 +307,9 @@ set_ivor:
> #ifdef CONFIG_PTE_64BIT
> #ifdef CONFIG_HUGETLB_PAGE
> #define FIND_PTE \
> - rlwinm r12, r10, 13, 19, 29; /* Compute pgdir/pmd offset */ \
> - lwzx r11, r12, r11; /* Get pgd/pmd entry */ \
> + rlwinm r12, r10, 14, 18, 28; /* Compute pgdir/pmd offset */ \
> + add r12, r11, r12;

You add the offset to pgdir?

> + lwz r11, 4(r12); /* Get pgd/pmd entry */ \

What is i offset 4?

--
Oscar Salvador
SUSE Labs