Re: [Xen-devel] [PATCH] xen/arm64: config: correct VMAP_VIRT_END

[Julien Grall <julien.grall@xxxxxxx>]

Hi Peng,

On 27/05/16 11:23, Peng Fan wrote:
> To ARM64, we should use '(VMAP_VIRT_START + GB(1))' as VMAP_VIRT_END,
s/To/For/

> but not '(VMAP_VIRT_START + GB(1) - 1)'.
>
> Seeing 'vm_end[type] = PFN_DOWN(end - start);' in vm_init_type,
> if not correct VMAP_VIRT_END, one page is wasted.
I find difficult to parse the commit message. How about:

"xen/arm64: config: Correctly define VMAP_VIRT_END

The vmap initialization code (vm_init_type) will round down the end of 
the region to a page-aligned address.
On ARM64, the default vmap region is located between 1G and 2G. Based on 
the initialization code, the end address is excluded of the region.
Therefore the current definition of VMAP_VIRT_END will lead the vmap 
code to not use the last 4K of the region.
Fix it by defining VMAP_VIRT_END as "VMAP_VIRT_START + GB(1)".
"

> Signed-off-by: Peng Fan <van.freenix@xxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
>
> I found X86 use '(VMAP_VIRT_START + GB(64))' and ARM32 use XENHEAP_VIRT_START,
> both are aligned address. So, I think ARM64 may also need to use aligned
> address. I am not very sure (:
Correct, this should be aligned to avoid wasting a page.

>   xen/include/asm-arm/config.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
> index 2d11b62..f92c0a0 100644
> --- a/xen/include/asm-arm/config.h
> +++ b/xen/include/asm-arm/config.h
> @@ -147,7 +147,7 @@
>   #define SLOT0_ENTRY_SIZE  SLOT0(1)
>
>   #define VMAP_VIRT_START  GB(1)
> -#define VMAP_VIRT_END    (VMAP_VIRT_START + GB(1) - 1)
> +#define VMAP_VIRT_END    (VMAP_VIRT_START + GB(1))
>
>   #define FRAMETABLE_VIRT_START  GB(32)
>   #define FRAMETABLE_SIZE        GB(32)
Regards,

--
Julien Grall

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