[PATCH v6 05/41] arm64: mm: Move fixmap region above vmemmap region

[Mark Rutland]

On Wed, Nov 29, 2023 at 12:16:01PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb at kernel.org>
> 
> Move the fixmap region above the vmemmap region, so that the start of
> the vmemmap delineates the end of the region available for vmalloc and
> vmap allocations and the randomized placement of the kernel and modules.
> 
> In a subsequent patch, we will take advantage of this to reclaim most of
> the vmemmap area when running a 52-bit VA capable build with 52-bit
> virtual addressing disabled at runtime.
> 
> Note that the existing guard region of 256 MiB covers the fixmap and PCI
> I/O regions as well, so we can reduce it 8 MiB, which is what we use in
> other places too.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>

As with the prior patch, this looks simple enough, but it'd be good if we could
do something to assert that we don't overlap this region with others.

Mark.

> ---
>  arch/arm64/include/asm/memory.h  | 2 +-
>  arch/arm64/include/asm/pgtable.h | 2 +-
>  arch/arm64/mm/ptdump.c           | 4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 99caeff78e1a..2745bed8ae5b 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -51,7 +51,7 @@
>  #define VMEMMAP_END		(VMEMMAP_START + VMEMMAP_SIZE)
>  #define PCI_IO_START		(VMEMMAP_END + SZ_8M)
>  #define PCI_IO_END		(PCI_IO_START + PCI_IO_SIZE)
> -#define FIXADDR_TOP		(VMEMMAP_START - SZ_32M)
> +#define FIXADDR_TOP		(-UL(SZ_8M))
>  
>  #if VA_BITS > 48
>  #define VA_BITS_MIN		(48)
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index b19a8aee684c..8d30e2787b1f 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -22,7 +22,7 @@
>   *	and fixed mappings
>   */
>  #define VMALLOC_START		(MODULES_END)
> -#define VMALLOC_END		(VMEMMAP_START - SZ_256M)
> +#define VMALLOC_END		(VMEMMAP_START - SZ_8M)
>  
>  #define vmemmap			((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
>  
> diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> index d1df56d44f8a..3958b008f908 100644
> --- a/arch/arm64/mm/ptdump.c
> +++ b/arch/arm64/mm/ptdump.c
> @@ -45,12 +45,12 @@ static struct addr_marker address_markers[] = {
>  	{ MODULES_END,			"Modules end" },
>  	{ VMALLOC_START,		"vmalloc() area" },
>  	{ VMALLOC_END,			"vmalloc() end" },
> -	{ FIXADDR_TOT_START,		"Fixmap start" },
> -	{ FIXADDR_TOP,			"Fixmap end" },
>  	{ VMEMMAP_START,		"vmemmap start" },
>  	{ VMEMMAP_START + VMEMMAP_SIZE,	"vmemmap end" },
>  	{ PCI_IO_START,			"PCI I/O start" },
>  	{ PCI_IO_END,			"PCI I/O end" },
> +	{ FIXADDR_TOT_START,		"Fixmap start" },
> +	{ FIXADDR_TOP,			"Fixmap end" },
>  	{ -1,				NULL },
>  };
>  
> -- 
> 2.43.0.rc1.413.gea7ed67945-goog
>