[kexec-lite PATCH] trampoline: Reset primary cpu endian to big-endian

[kexec-lite PATCH] trampoline: Reset primary cpu endian to big-endian

[Samuel Mendoza-Jonas]

Older big-endian ppc64 kernels don't include the FIXUP_ENDIAN check,
meaning if we kexec from a little-endian kernel the target kernel will
fail to boot.
Returning to big-endian before we enter the target kernel ensures that
the target kernel can boot whether or not it includes FIXUP_ENDIAN.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
---
 kexec_trampoline.S |  9 ++++++++-
 kexec_trampoline.h | 17 +++++++++++++++--
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/kexec_trampoline.S b/kexec_trampoline.S
index a3eb314..29537ab 100644
--- a/kexec_trampoline.S
+++ b/kexec_trampoline.S
@@ -41,6 +41,8 @@
 #define	r7	7
 #define	r8	8
 #define	r9	9
+#define	r10	10
+#define	r11	11
 
 #ifdef __powerpc64__
 #define LOAD	ld
@@ -50,8 +52,10 @@
 
 #if defined(__LITTLE_ENDIAN__)
 #define STWX_BE	stwbrx
+#define BCTR .long 0x2004804e
 #elif defined(__BIG_ENDIAN__)
 #define STWX_BE	stwx
+#define BCTR bctr
 #else
 #error no endianness defined!
 #endif
@@ -89,7 +93,10 @@ start:
 	li	r5,0
 
 	mtctr	r4
-	bctr
+
+	RESET_ENDIAN
+
+	BCTR
 
 . = KERNEL_ADDR_OFFSET
 kernel_addr:
diff --git a/kexec_trampoline.h b/kexec_trampoline.h
index 6485c88..909953b 100644
--- a/kexec_trampoline.h
+++ b/kexec_trampoline.h
@@ -27,7 +27,20 @@
 /* Fixed offset in device tree for storing the physical ID of the boot CPU */
 #define DT_CPU_OFFSET			28
 
-#ifndef __ASSEMBLY__
+#ifdef __ASSEMBLY__
+#define RESET_ENDIAN						   \
+	mfmsr	r9;						   \
+	clrldi.	r10,r9,63;					   \
+	beq	$+36;		/* Already big-endian */	   \
+	bcl	20,31,$+4;					   \
+	mflr	r10;						   \
+	addi	r10,r10,28;					   \
+	mfmsr	r11;						   \
+	xori	r11,r11,1;					   \
+	mtsrr0	r10;						   \
+	mtsrr1	r11;						   \
+	rfid;
+#else
 
 extern char __trampoline_start[];
 extern char __trampoline_end[];
@@ -48,6 +61,6 @@ static inline void trampoline_set_device_tree(void *p, unsigned long addr)
 	*v = addr;
 }
 
-#endif
+#endif /* !__ASSEMBLY__ */
 
 #endif
-- 
2.4.5

Re: [kexec-lite PATCH] trampoline: Reset primary cpu endian to big-endian

[Anton Blanchard]

Hi Sam,

> Older big-endian ppc64 kernels don't include the FIXUP_ENDIAN check,
> meaning if we kexec from a little-endian kernel the target kernel will
> fail to boot.
> Returning to big-endian before we enter the target kernel ensures that
> the target kernel can boot whether or not it includes FIXUP_ENDIAN.

Thanks!

I wonder if we can do something simpler, and always enter via rfid.
Avoids the need for the endian trampoline. Something like:

  	mtsrr0	r4

	mfmsr	r5
	clrrdi	r5,r5,1 	/* Clear MSR_LE */
	mtsrr1	r5

	li	r5,0

	rfid

Anton

Re: [kexec-lite PATCH] trampoline: Reset primary cpu endian to big-endian

[Samuel Mendoza-Jonas]

On 08/07/15 11:56, Anton Blanchard wrote:
> Hi Sam,
> 
>> Older big-endian ppc64 kernels don't include the FIXUP_ENDIAN check,
>> meaning if we kexec from a little-endian kernel the target kernel will
>> fail to boot.
>> Returning to big-endian before we enter the target kernel ensures that
>> the target kernel can boot whether or not it includes FIXUP_ENDIAN.
> 
> Thanks!
> 
> I wonder if we can do something simpler, and always enter via rfid.
> Avoids the need for the endian trampoline. Something like:
> 
>   	mtsrr0	r4
> 
> 	mfmsr	r5
> 	clrrdi	r5,r5,1 	/* Clear MSR_LE */
> 	mtsrr1	r5
> 
> 	li	r5,0
> 
> 	rfid
> 
> Anton
> 

Ah that's a neat idea, I'll test and send a V2.

Cheers,
Sam

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