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Subject: Re: [PATCH v1 16/46] powerpc/mm: Allocate static page tables for
 fixmap
From:   Christophe Leroy <christophe.leroy@c-s.fr>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <cover.1584360343.git.christophe.leroy@c-s.fr>
 <d4bd46fe0103f8a8cb7e5affb2a7fcc3185be24e.1584360344.git.christophe.leroy@c-s.fr>
Message-ID: <b9c92137-f757-1e6a-bca9-5c522e1083c5@c-s.fr>
Date:   Tue, 17 Mar 2020 15:38:46 +0100
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Le 16/03/2020 à 13:36, Christophe Leroy a écrit :
> Allocate static page tables for the fixmap area. This allows
> setting mappings through page tables before memblock is ready.
> That's needed to use early_ioremap() early and to use standard
> page mappings with fixmap.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>   arch/powerpc/include/asm/fixmap.h |  4 ++++
>   arch/powerpc/kernel/setup_32.c    |  2 +-
>   arch/powerpc/mm/pgtable_32.c      | 16 ++++++++++++++++
>   3 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/fixmap.h b/arch/powerpc/include/asm/fixmap.h
> index 2ef155a3c821..ccbe2e83c950 100644
> --- a/arch/powerpc/include/asm/fixmap.h
> +++ b/arch/powerpc/include/asm/fixmap.h
> @@ -86,6 +86,10 @@ enum fixed_addresses {
>   #define __FIXADDR_SIZE	(__end_of_fixed_addresses << PAGE_SHIFT)
>   #define FIXADDR_START		(FIXADDR_TOP - __FIXADDR_SIZE)
>   
> +#define FIXMAP_ALIGNED_SIZE	(ALIGN(FIXADDR_TOP, PGDIR_SIZE) - \
> +				 ALIGN_DOWN(FIXADDR_START, PGDIR_SIZE))
> +#define FIXMAP_PTE_SIZE	(FIXMAP_ALIGNED_SIZE / PGDIR_SIZE * PTE_TABLE_SIZE)
> +
>   #define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_NCG
>   #define FIXMAP_PAGE_IO	PAGE_KERNEL_NCG
>   
> diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
> index 5b49b26eb154..3f1e1c0b328a 100644
> --- a/arch/powerpc/kernel/setup_32.c
> +++ b/arch/powerpc/kernel/setup_32.c
> @@ -81,7 +81,7 @@ notrace void __init machine_init(u64 dt_ptr)
>   	/* Configure static keys first, now that we're relocated. */
>   	setup_feature_keys();
>   
> -	early_ioremap_setup();
> +	early_ioremap_init();
>   
>   	/* Enable early debugging if any specified (see udbg.h) */
>   	udbg_early_init();
> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index f62de06e3d07..9934659cb871 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -29,11 +29,27 @@
>   #include <asm/fixmap.h>
>   #include <asm/setup.h>
>   #include <asm/sections.h>
> +#include <asm/early_ioremap.h>
>   
>   #include <mm/mmu_decl.h>
>   
>   extern char etext[], _stext[], _sinittext[], _einittext[];
>   
> +static u8 early_fixmap_pagetable[FIXMAP_PTE_SIZE] __page_aligned_data;

Sparse reports this as a variable size array. This is definitely not. 
Gcc properly sees it is an 8k table (2 pages).

Christophe


> +
> +notrace void __init early_ioremap_init(void)
> +{
> +	unsigned long addr = ALIGN_DOWN(FIXADDR_START, PGDIR_SIZE);
> +	pte_t *ptep = (pte_t *)early_fixmap_pagetable;
> +	pmd_t *pmdp = pmd_ptr_k(addr);
> +
> +	for (; (s32)(FIXADDR_TOP - addr) > 0;
> +	     addr += PGDIR_SIZE, ptep += PTRS_PER_PTE, pmdp++)
> +		pmd_populate_kernel(&init_mm, pmdp, ptep);
> +
> +	early_ioremap_setup();
> +}
> +
>   static void __init *early_alloc_pgtable(unsigned long size)
>   {
>   	void *ptr = memblock_alloc(size, size);
> 

Christophe