Re: [Xen-devel] [PATCH 3/3] xen: arm: rework dom0 initrd and dtb placement

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-04-09 at 14:09 +0100, Julien Grall wrote:
> On 04/09/2014 01:57 PM, Ian Campbell wrote:
> > On Wed, 2014-04-09 at 13:54 +0100, Julien Grall wrote:
> >> Hi Ian,
> >>
> >> On 04/09/2014 12:51 PM, Ian Campbell wrote:
> >>> This now uses the same decision tree as libxc (which is much easier to 
> >>> test).
> >>>
> >>> The main change is to explictly handle the placement at 128MB or end of 
> >>> RAM as
> >>
> >> s/explictly/explicitly/
> >> s/mopules/modules/
> > 
> > Gah, fingers not working right today it seems.
> > 
> >>> since it is redundant with the case where placing them at the end of RAM 
> >>> ends
> >>> up abutting the kernel.
> >>>
> >>> Also round the kernel size up to a 2MB boundary.
> >>
> >> A bit surprised that it was not done before :).
> > 
> > Me too.
> > 
> >>> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >>> ---
> >>> I'm sure to regret playing with this yet again...
> >>> ---
> >>>  xen/arch/arm/kernel.c |   22 ++++++++++++----------
> >>>  1 file changed, 12 insertions(+), 10 deletions(-)
> >>>
> >>> diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c
> >>> index bc625a4..1102392 100644
> >>> --- a/xen/arch/arm/kernel.c
> >>> +++ b/xen/arch/arm/kernel.c
> >>> @@ -77,7 +77,7 @@ static void place_modules(struct kernel_info *info,
> >>>      const paddr_t rambase = info->mem.bank[0].start;
> >>>      const paddr_t ramsize = info->mem.bank[0].size;
> >>>      const paddr_t ramend = rambase + ramsize;
> >>> -    const paddr_t kernsize = kernend - kernbase;
> >>> +    const paddr_t kernsize = ROUNDUP(kernend, MB(2)) - kernbase;
> >>
> >> You are using ROUNDUP(kernend, MB(2)) in few places, why didn't you
> >> roundup directly kernend?
> > 
> > It's passed as a paramter, and it's not possible to round it before
> > using it here (code before declarations), so I'd have to make kernsize
> > non-const and initialise it after the rounding. I didn't think it was
> > worth it.
> 
> In this case I'm lost... You are mixing kernend and ROUNDUP(kernend, MB(2)).
> 
> As I understand, we don't need to round up on the second if expression
> (see code below).

It ensures that the modules don't start until at least the 2M boundary
after the kernel's end. The userspace side does the same.

Whether that's really worthwhile I don't know.

> 
> +    if ( ramend >= ram128mb + modsize && kernend < ram128mb )
> +        modbase = ram128mb;
> +    else if ( ramend - modsize > ROUNDUP(kernend, MB(2)) )
> +        modbase = ramend - modsize;
> +    else if ( kernbase - rambase > modsize )
> 
> Regards,
> 



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