[Xen-devel] [PATCH] xen: arm: load FDT below 0.5G

[Ian Campbell <ijc@xxxxxxxxxxxxxx>]

From: Ian Campbell <ian.campbell@xxxxxxxxxx>

The 32-bit Linux kernel uses its lowmem direct mapping to access the FDT. The
lowmem mapping is around 3/4GiB but varies depending on the kernel's .config.
Use a limit of 1/2G to be safe.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/domain_build.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 056c9df..ff9e679 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -504,13 +504,14 @@ static int prepare_dtb(struct domain *d, struct 
kernel_info *kinfo)
         goto err;
 
     /*
-     * DTB must be load below 4GiB and far enough from linux (Linux uses
-     * the space after it to decompress)
-     * Load the DTB at the end of the first bank, while ensuring it is
-     * also below 4G
+     * DTB must be loaded below around 0.5GiB and far enough from
+     * linux (Linux uses the space after it to decompress).
+     *
+     * Load the DTB as high as possible in the first bank, while
+     * ensuring it is also below 0.5G
      */
     end = kinfo->mem.bank[0].start + kinfo->mem.bank[0].size;
-    end = MIN(1ull << 32, end);
+    end = MIN(kinfo->mem.bank[0].start + (1ull << 29), end);
     kinfo->dtb_paddr = end - fdt_totalsize(kinfo->fdt);
     /* Align the address to 2Mb. Linux only requires 4 byte alignment */
     kinfo->dtb_paddr &= ~((2 << 20) - 1);
-- 
1.8.3.2


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