Patch "powerpc: Fix definition of SIAR and SDAR registers" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

powerpc: Fix definition of SIAR and SDAR registers

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-fix-definition-of-siar-and-sdar-registers.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Huth <[email protected]>
Date: Thu, 12 May 2016 13:26:44 +0200
Subject: powerpc: Fix definition of SIAR and SDAR registers

From: Thomas Huth <[email protected]>

commit d23fac2b27d94aeb7b65536a50d32bfdc21fe01e upstream.

The SIAR and SDAR registers are available twice, one time as SPRs 780 / 781 (unprivileged, but read-only), and one time as the SPRs 796 / 797 (privileged, but read and write). The Linux kernel code currently uses the unprivileged SPRs - while this is OK for reading, writing to that register of course does not work.
Since the KVM code tries to write to this register, too (see the mtspr in book3s_hv_rmhandlers.S), the contents of this register sometimes get lost for the guests, e.g. during migration of a VM.
To fix this issue, simply switch to the privileged SPR numbers instead.

---
 arch/powerpc/include/asm/reg.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -744,13 +744,13 @@
 #define SPRN_PMC6	792
 #define SPRN_PMC7	793
 #define SPRN_PMC8	794
-#define SPRN_SIAR	780
-#define SPRN_SDAR	781
 #define SPRN_SIER	784
 #define   SIER_SIPR		0x2000000	/* Sampled MSR_PR */
 #define   SIER_SIHV		0x1000000	/* Sampled MSR_HV */
 #define   SIER_SIAR_VALID	0x0400000	/* SIAR contents valid */
 #define   SIER_SDAR_VALID	0x0200000	/* SDAR contents valid */
+#define SPRN_SIAR	796
+#define SPRN_SDAR	797
 #define SPRN_TACR	888
 #define SPRN_TCSCR	889
 #define SPRN_CSIGR	890

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/powerpc-fix-definition-of-siar-and-sdar-registers.patch queue-4.4/powerpc-use-privileged-spr-number-for-mmcr2.patch queue-4.4/powerpc-pseries-add-power8nvl-support-to-ibm-client-architecture-support-call.patch