[PATCH 1/2] powerpc/book3s64/kexec: Clear CIABR on kexec

[PATCH 1/2] powerpc/book3s64/kexec: Clear CIABR on kexec

[Jordan Niethe]

The value in CIABR persists across kexec which can lead to unintended
results when the new kernel hits the old kernel's breakpoint. For
example:

0:mon> bi $loadavg_proc_show
0:mon> b
   type            address
1 inst   c000000000519060  loadavg_proc_show+0x0/0x130
0:mon> x

$ kexec -l /mnt/vmlinux --initrd=/mnt/rootfs.cpio.gz --append='xmon=off'
$ kexec -e

$ cat /proc/loadavg
Trace/breakpoint trap

Make sure CIABR is cleared so this does not happen.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
 arch/powerpc/include/asm/book3s/64/kexec.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/kexec.h b/arch/powerpc/include/asm/book3s/64/kexec.h
index 6b5c3a248ba2..d4b9d476ecba 100644
--- a/arch/powerpc/include/asm/book3s/64/kexec.h
+++ b/arch/powerpc/include/asm/book3s/64/kexec.h
@@ -3,6 +3,7 @@
 #ifndef _ASM_POWERPC_BOOK3S_64_KEXEC_H_
 #define _ASM_POWERPC_BOOK3S_64_KEXEC_H_
 
+#include <asm/plpar_wrappers.h>
 
 #define reset_sprs reset_sprs
 static inline void reset_sprs(void)
@@ -14,6 +15,10 @@ static inline void reset_sprs(void)
 
 	if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
 		mtspr(SPRN_IAMR, 0);
+		if (cpu_has_feature(CPU_FTR_HVMODE))
+			mtspr(SPRN_CIABR, 0);
+		else
+			plpar_set_ciabr(0);
 	}
 
 	/*  Do we need isync()? We are going via a kexec reset */
-- 
2.17.1

[PATCH 2/2] powerpc/powernv/idle: Restore CIABR after idle for Power9

[Jordan Niethe]

On Power9, CIABR is lost after idle. This means that instruction
breakpoints set by xmon which use CIABR do not work. Fix this by
restoring CIABR after idle.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
 arch/powerpc/platforms/powernv/idle.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 1ed7c5286487..e6f461812856 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -589,6 +589,7 @@ struct p9_sprs {
 	u64 spurr;
 	u64 dscr;
 	u64 wort;
+	u64 ciabr;
 
 	u64 mmcra;
 	u32 mmcr0;
@@ -668,6 +669,7 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
 		sprs.spurr	= mfspr(SPRN_SPURR);
 		sprs.dscr	= mfspr(SPRN_DSCR);
 		sprs.wort	= mfspr(SPRN_WORT);
+		sprs.ciabr	= mfspr(SPRN_CIABR);
 
 		sprs.mmcra	= mfspr(SPRN_MMCRA);
 		sprs.mmcr0	= mfspr(SPRN_MMCR0);
@@ -785,6 +787,7 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
 	mtspr(SPRN_SPURR,	sprs.spurr);
 	mtspr(SPRN_DSCR,	sprs.dscr);
 	mtspr(SPRN_WORT,	sprs.wort);
+	mtspr(SPRN_CIABR,	sprs.ciabr);
 
 	mtspr(SPRN_MMCRA,	sprs.mmcra);
 	mtspr(SPRN_MMCR0,	sprs.mmcr0);
-- 
2.17.1

Re: [PATCH 1/2] powerpc/book3s64/kexec: Clear CIABR on kexec

[Michael Ellerman]

On Mon, 7 Dec 2020 12:05:18 +1100, Jordan Niethe wrote:
> The value in CIABR persists across kexec which can lead to unintended
> results when the new kernel hits the old kernel's breakpoint. For
> example:
> 
> 0:mon> bi $loadavg_proc_show
> 0:mon> b
>    type            address
> 1 inst   c000000000519060  loadavg_proc_show+0x0/0x130
> 0:mon> x
> 
> [...]

Applied to powerpc/next.

[1/2] powerpc/book3s64/kexec: Clear CIABR on kexec
      https://git.kernel.org/powerpc/c/4bb3219837a3dcf58bce96c27db6e0cd48f3d9b2
[2/2] powerpc/powernv/idle: Restore CIABR after idle for Power9
      https://git.kernel.org/powerpc/c/250ad7a45b1e58d580decfb935fc063c4cf56f91

cheers