x86: fix spontaneous reboot with allyesconfig bzImage
recently the 64-bit allyesconfig bzImage kernel started spontaneously
rebooting during early bootup.
after a few fun hours spent with early init debugging, it turns out
that we've got this rather annoying limit on the size of the kernel
image:
#define KERNEL_TEXT_SIZE (40*1024*1024)
which limit my vmlinux just happened to pass:
text data bss dec hex filename
29703744 4222751 8646224 42572719 2899baf vmlinux
40 MB is 42572719 bytes, so my vmlinux was just 1.5% above this limit :-/
So it happily crashed right in head_64.S, which - as we all know - is
the most debuggable code in the whole architecture ;-)
So increase the limit to allow an up to 128MB kernel image to be mapped.
(should anyone be that crazy or lazy)
We have a full 4K of pagetable (level2_kernel_pgt) allocated for these
mappings already, so there's no RAM overhead and the limit was rather
pointless and arbitrary.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index eb41504..b037b15 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -379,18 +379,24 @@
/* Since I easily can, map the first 1G.
* Don't set NX because code runs from these pages.
*/
- PMDS(0x0000000000000000, __PAGE_KERNEL_LARGE_EXEC, PTRS_PER_PMD)
+ PMDS(0, __PAGE_KERNEL_LARGE_EXEC, PTRS_PER_PMD)
NEXT_PAGE(level2_kernel_pgt)
- /* 40MB kernel mapping. The kernel code cannot be bigger than that.
- When you change this change KERNEL_TEXT_SIZE in page.h too. */
- /* (2^48-(2*1024*1024*1024)-((2^39)*511)-((2^30)*510)) = 0 */
- PMDS(0x0000000000000000, __PAGE_KERNEL_LARGE_EXEC|_PAGE_GLOBAL, KERNEL_TEXT_SIZE/PMD_SIZE)
- /* Module mapping starts here */
- .fill (PTRS_PER_PMD - (KERNEL_TEXT_SIZE/PMD_SIZE)),8,0
+ /*
+ * 128 MB kernel mapping. We spend a full page on this pagetable
+ * anyway.
+ *
+ * The kernel code+data+bss must not be bigger than that.
+ *
+ * (NOTE: at +128MB starts the module area, see MODULES_VADDR.
+ * If you want to increase this then increase MODULES_VADDR
+ * too.)
+ */
+ PMDS(0, __PAGE_KERNEL_LARGE_EXEC|_PAGE_GLOBAL,
+ KERNEL_TEXT_SIZE/PMD_SIZE)
NEXT_PAGE(level2_spare_pgt)
- .fill 512,8,0
+ .fill 512, 8, 0
#undef PMDS
#undef NEXT_PAGE
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 6dbb003..a02a14f 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -172,8 +172,9 @@
}
/*
- * The head.S code sets up the kernel high mapping from:
- * __START_KERNEL_map to __START_KERNEL_map + KERNEL_TEXT_SIZE
+ * The head.S code sets up the kernel high mapping:
+ *
+ * from __START_KERNEL_map to __START_KERNEL_map + size (== _end-_text)
*
* phys_addr holds the negative offset to the kernel, which is added
* to the compile time generated pmds. This results in invalid pmds up