path: root/arch/arm64/include/asm/page.h
diff options
authorMark Rutland <>2014-06-24 16:51:35 +0100
committerCatalin Marinas <>2014-07-10 12:36:12 +0100
commitbd00cd5f8c8c3c282bb1e1eac6a6679a4f808091 (patch)
treef146d737e7fdd6b107e23f51cd912402ef7f0bcd /arch/arm64/include/asm/page.h
parent909a4069da65a5cfca8c968edf9f0d99f694d2f3 (diff)
arm64: place initial page tables above the kernel
Currently we place swapper_pg_dir and idmap_pg_dir below the kernel image, between PHYS_OFFSET and (PHYS_OFFSET + TEXT_OFFSET). However, bootloaders may use portions of this memory below the kernel and we do not parse the memory reservation list until after the MMU has been enabled. As such we may clobber some memory a bootloader wishes to have preserved. To enable the use of all of this memory by bootloaders (when the required memory reservations are communicated to the kernel) it is necessary to move our initial page tables elsewhere. As we currently have an effectively unbound requirement for memory at the end of the kernel image for .bss, we can place the page tables here. This patch moves the initial page table to the end of the kernel image, after the BSS. As they do not consist of any initialised data they will be stripped from the kernel Image as with the BSS. The BSS clearing routine is updated to stop at __bss_stop rather than _end so as to not clobber the page tables, and memory reservations made redundant by the new organisation are removed. Signed-off-by: Mark Rutland <> Tested-by: Laura Abbott <> Acked-by: Will Deacon <> Signed-off-by: Catalin Marinas <>
Diffstat (limited to 'arch/arm64/include/asm/page.h')
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
index 46bf66628b6a..a6331e6a92b5 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -31,6 +31,15 @@
/* We do define AT_SYSINFO_EHDR but don't use the gate mechanism */
+ * The idmap and swapper page tables need some space reserved in the kernel
+ * image. The idmap only requires a pgd and a next level table to (section) map
+ * the kernel, while the swapper also maps the FDT and requires an additional
+ * table to map an early UART. See __create_page_tables for more information.
+ */
#ifndef __ASSEMBLY__