[PATCH] xen: arm: Document xenheap_megabytes limitation

[PATCH] xen: arm: Document xenheap_megabytes limitation

[Chris (Christopher) Brand]

In setup_mm(), the value passed as xenheap_megabytes gets
converted to pages and passed to setup_xenheap_mappings(),
which in turn passes it to create_32mb_mappings(), which
contains an ASSERT that the value passed is a multiple of
32MB. So specifying any value that is not an integer multiple
of 32 will cause Xen to hit this assert and fail to boot.

Signed-off-by: Chris Brand <chris.brand@broadcom.com>
---
 docs/misc/xen-command-line.markdown | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index 4889e27626d4..f3d3bd6ce56a 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -242,7 +242,7 @@ the NMI watchdog is also enabled.
 
 > Default: `0` (1/32 of RAM)
 
-Amount of RAM to set aside for the Xenheap.
+Amount of RAM to set aside for the Xenheap. Must be an integer multiple of 32.
 
 By default will use 1/32 of the RAM up to a maximum of 1GB and with a
 minimum of 32M, subject to a suitably aligned and sized contiguous
-- 
1.9.1

Re: [PATCH] xen: arm: Document xenheap_megabytes limitation

[Julien Grall]

Hi Chris,

Thank you for patch.

On 23/07/15 17:31, Chris (Christopher) Brand wrote:
> In setup_mm(), the value passed as xenheap_megabytes gets
> converted to pages and passed to setup_xenheap_mappings(),
> which in turn passes it to create_32mb_mappings(), which
> contains an ASSERT that the value passed is a multiple of
> 32MB. So specifying any value that is not an integer multiple
> of 32 will cause Xen to hit this assert and fail to boot.
> 
> Signed-off-by: Chris Brand <chris.brand@broadcom.com>

I wondering if it would worth to add a check in the code to ensure that
it's a multiple of 32MB?

Nonetheless:

Reviewed-by: Julien Grall <julien.grall@citrix.com>

> ---
>  docs/misc/xen-command-line.markdown | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
> index 4889e27626d4..f3d3bd6ce56a 100644
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -242,7 +242,7 @@ the NMI watchdog is also enabled.
>  
>  > Default: `0` (1/32 of RAM)
>  
> -Amount of RAM to set aside for the Xenheap.
> +Amount of RAM to set aside for the Xenheap. Must be an integer multiple of 32.
>  
>  By default will use 1/32 of the RAM up to a maximum of 1GB and with a
>  minimum of 32M, subject to a suitably aligned and sized contiguous
> 


Regards,

-- 
Julien Grall

Re: [PATCH] xen: arm: Document xenheap_megabytes limitation

[Ian Campbell]

On Thu, 2015-07-23 at 17:49 +0100, Julien Grall wrote:
> Hi Chris,
> 
> Thank you for patch.
> 
> On 23/07/15 17:31, Chris (Christopher) Brand wrote:
> > In setup_mm(), the value passed as xenheap_megabytes gets
> > converted to pages and passed to setup_xenheap_mappings(),
> > which in turn passes it to create_32mb_mappings(), which
> > contains an ASSERT that the value passed is a multiple of
> > 32MB. So specifying any value that is not an integer multiple
> > of 32 will cause Xen to hit this assert and fail to boot.
> > 
> > Signed-off-by: Chris Brand <chris.brand@broadcom.com>
> 
> I wondering if it would worth to add a check in the code to ensure 
> that
> it's a multiple of 32MB?

Arguably we have that in the form of the assert/panic, but perhaps
there should be a nicer message.

> Nonetheless:
> 
> Reviewed-by: Julien Grall <julien.grall@citrix.com>

Acked + applied.