Increase kernel text size for x86_64

Hi all,

I cannot load a x86_64 kernel with kexec on 2.6.31; the error message is:

Can't find kernel text map area from kcore
Cannot load /boot/vmlinuz

Digging through the source I found a mismatch between the assumed kernel text size; kexec has:

#define KERNEL_TEXT_SIZE (40UL*1024*1024)

but on the kernel side we have:

include/asm/page_64_types.h:
#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)

And, indeed, changing the definition in kexec-tools to the kernel one fixed the problem.

Not sure if this has been reported before, if so please ignore the noise.

Quoted 14 lines · Hannes Reinecke

Hi all,

I cannot load a x86_64 kernel with kexec on 2.6.31; the error message is:

Can't find kernel text map area from kcore
Cannot load /boot/vmlinuz

Digging through the source I found a mismatch between the assumed kernel text size; kexec has:

#define KERNEL_TEXT_SIZE (40UL*1024*1024)

but on the kernel side we have:

Quoted 8 lines

include/asm/page_64_types.h:
#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)

And, indeed, changing the definition in kexec-tools to the kernel one fixed the problem.

Not sure if this has been reported before, if so please ignore the noise.

Hi,

I'm wondering what effect this would have when using kexec-tools with older kernels, which presumably have a smaller value for KERNEL_IMAGE_SIZE.

Quoted 7 lines

kexec/arch/x86_64/crashdump-x86_64.h +0 -0

index 9f4dee9..0e83527 100644
@@ -11,7 +11,7 @@ int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline,
 #define MAXMEM           0x3fffffffffffUL
 

kexec/arch/x86_64/crashdump-x86_64.h int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline, · line 17

Quoted 6 lines

kexec/arch/x86_64/crashdump-x86_64.h +1 -1

 /* Kernel text size */
-#define KERNEL_TEXT_SIZE  (40UL*1024*1024)
+#define KERNEL_TEXT_SIZE  (512UL*1024*1024)
 
 #define CRASH_MAX_MEMMAP_NR	(KEXEC_MAX_SEGMENTS + 1)
 #define CRASH_MAX_MEMORY_RANGES	(MAX_MEMORY_RANGES + 2)

Quoted 37 lines · Simon Horman

Quoted 14 lines · Hannes Reinecke

Hi all,

I cannot load a x86_64 kernel with kexec on 2.6.31; the error message is:

Can't find kernel text map area from kcore
Cannot load /boot/vmlinuz

Digging through the source I found a mismatch between the assumed kernel text size; kexec has:

#define KERNEL_TEXT_SIZE (40UL*1024*1024)

but on the kernel side we have:

Quoted 8 lines

include/asm/page_64_types.h:
#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)

And, indeed, changing the definition in kexec-tools to the kernel one fixed the problem.

Not sure if this has been reported before, if so please ignore the noise.

Hi,

I'm wondering what effect this would have when using kexec-tools with older kernels, which presumably have a smaller value for KERNEL_IMAGE_SIZE.

Quoted 7 lines

kexec/arch/x86_64/crashdump-x86_64.h +0 -0

index 9f4dee9..0e83527 100644
@@ -11,7 +11,7 @@ int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline,
 #define MAXMEM           0x3fffffffffffUL
 

Quoted 7 lines

kexec/arch/x86_64/crashdump-x86_64.h int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline, · line 17

Quoted 6 lines

kexec/arch/x86_64/crashdump-x86_64.h +1 -1

 /* Kernel text size */
-#define KERNEL_TEXT_SIZE  (40UL*1024*1024)
+#define KERNEL_TEXT_SIZE  (512UL*1024*1024)
 
 #define CRASH_MAX_MEMMAP_NR	(KEXEC_MAX_SEGMENTS + 1)
 #define CRASH_MAX_MEMORY_RANGES	(MAX_MEMORY_RANGES + 2)

Well, the actual point of failure is in kexec/arch/x86_64/crashdump-x86_64.c:125

			/* Look for kernel text mapping header. */
			if ((saddr >= __START_KERNEL_map) &&
			    (eaddr <= __START_KERNEL_map + KERNEL_TEXT_SIZE)) {
				saddr = (saddr) & (~(KERN_VADDR_ALIGN - 1));
				info->kern_vaddr_start = saddr;
				size = eaddr - saddr;

which basically should look for a ELF header into which the kernel fits. As we're effectively just moving the upper limit I fail to see any harm to older kernels.

Hmm. Haven't checked for other occurrences of KERNEL_TEXT_SIZE, though.

Would be nice we could be getting these values off somewhere; rely on some kernel defines is going to break now and then.