Re: [PATCH] xen/arm64: Fix incorrect DIRECTMAP_SIZE calculation

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

It is not clear to me why this was sent In-reply-to the other patch. If 
they are meant to form a series, then this should have a cover letter + 
each patch should be numbered.
If they are truly separate, then please don't thread them.

On 16/01/2023 14:41, Michal Orzel wrote:
> The direct mapped area occupies L0 slots from 256 to 265 (i.e. 10 slots),
I would write "265 included"  or similar so it shows why this is a problem.

> resulting in 5TB (512GB * 10) of virtual address space. However, due to
> incorrect slot subtraction (we take 9 slots into account) we set
> DIRECTMAP_SIZE to 4.5TB instead. Fix it.
I would clarify that we only support up to 2TB. So this is a latent 
issue. This would make clear that...
> Fixes: 5263507b1b4a ("xen: arm: Use a direct mapping of RAM on arm64")
... while this is fixing a bug, it is not going to be a candidate for 
backport.
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
>   xen/arch/arm/include/asm/config.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/include/asm/config.h 
> b/xen/arch/arm/include/asm/config.h
> index 0fefed1b8aa9..16213c8b677f 100644
> --- a/xen/arch/arm/include/asm/config.h
> +++ b/xen/arch/arm/include/asm/config.h
> @@ -157,7 +157,7 @@
>   #define FRAMETABLE_NR          (FRAMETABLE_SIZE / sizeof(*frame_table))
>   
>   #define DIRECTMAP_VIRT_START   SLOT0(256)
> -#define DIRECTMAP_SIZE         (SLOT0_ENTRY_SIZE * (265-256))
> +#define DIRECTMAP_SIZE         (SLOT0_ENTRY_SIZE * (266 - 256))
>   #define DIRECTMAP_VIRT_END     (DIRECTMAP_VIRT_START + DIRECTMAP_SIZE - 1)
>   
>   #define XENHEAP_VIRT_START     directmap_virt_start
Cheers,

--
Julien Grall