Re: [Xen-devel] [PATCH] libxc/arm: align to page size the base address of the device tree

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/20/2013 01:13 PM, Ian Campbell wrote:
> On Wed, 2013-11-20 at 13:04 +0000, Julien Grall wrote:
> > On 11/20/2013 09:48 AM, Ian Campbell wrote:
> > > On Tue, 2013-11-19 at 18:52 +0000, Julien Grall wrote:
> > > > xc_dom_alloc_segment requires start address to be page align.
> > > I wonder why I didn't see this? It seems very unlikely that my dtb would
> > > be exactly page sized, yet it works... Ah, I have >128M of RAM in my
> > > guest so the base would be 128M. Well spotted.
> > >
> > > I think it would be slightly preferable to round dtbsize up to a page.
> > > e.g. the following. What do you think?
> > Sounds good to me. I wrote my patch in the other way because I though
> > RAM size can be non-page aligned.
> That would be concern except the sizes are defined immediately above as
> shifts based on page numbers.
>
> > > 8>------------------
> > >
> > >   From 079a2815d86567de1cbb541541d08a0b9ac3d18d Mon Sep 17 00:00:00 2001
> > > From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > > Date: Wed, 20 Nov 2013 09:45:32 +0000
> > > Subject: [PATCH] libxl: arm: ensure DTB is page aligned
> > >
> > > xc_dom_alloc_segment requires this. Since rambase and ramend are both page
> > > aligned, rounding up the DTB is sufficient.
> > >
> > > Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > > ---
> > >    tools/libxc/xc_dom_arm.c |    2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
> > > index ffe575b..a40e04d 100644
> > > --- a/tools/libxc/xc_dom_arm.c
> > > +++ b/tools/libxc/xc_dom_arm.c
> > > @@ -282,7 +282,7 @@ int arch_setup_meminit(struct xc_dom_image *dom)
> > >        {
> > >            const uint64_t rambase = dom->rambase_pfn << XC_PAGE_SHIFT;
> > >            const uint64_t ramend = rambase + ( dom->total_pages << 
> > > XC_PAGE_SHIFT );
> > > -        const uint64_t dtbsize = ( dom->devicetree_size + 3 ) & ~0x3;
> > > +        const uint64_t dtbsize = ROUNDUP(dom->devicetree_size, XC_PAGE_SHIFT);
> > XC_PAGE_SHIFT only contains the shift. You should use XC_PAGE_SIZE.
> That's not how ROUNDUP is defined in libxc:
> #define ROUNDUP(_x,_w) (((unsigned long)(_x)+(1UL<<(_w))-1) & ~((1UL<<(_w))-1))
>
> so it expects _w (width?) to be the shift.
Oh right, I though it was defined as in xen. In any case, I think you 
should use XC_DOM_PAGE_SHIFT(dom).
--
Julien Grall

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