The SIAR register is available twice, one time as SPR 780 (unprivileged,
but read-only), and one time as SPR 796 (privileged, but read and write).
The Linux kernel code currently uses SPR 780 - and 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 other SPR numer 796 instead.
Signed-off-by: Thomas Huth <th...@redhat.com>
---
Note: The perf code in core-book3s.c also seems to write to the SIAR
SPR, so that might be affected by this issue, too - but I did
not test the perf code, so I'm not sure about that part.
arch/powerpc/include/asm/reg.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index f5f4c66..6630420 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -752,13 +752,13 @@
#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_TACR 888
#define SPRN_TCSCR 889
#define SPRN_CSIGR 890
--
1.8.3.1
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