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

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.


  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 << 
-        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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