[PATCH] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop.

["Gautham R. Shenoy" <ego@linux.vnet.ibm.com>]

From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

On 64-bit Servers, SPRN_SPRG3 and its userspace read-only mirror
SPRN_USPRG3 are used as userspace VDSO write and read registers
respectively.

SPRN_SPRG3 is lost when we enter stop4 and above, and is currently not
restored.  As a result, any read from SPRN_USPRG3 returns zero on an
exit from stop4 and above.

Thus in this situation, any call from sched_getcpu() always returns
zero, as on powerpc, we call __kernel_getcpu() which relies upon
SPRN_USPRG3 to report the CPU and NUMA node information.

Fix this by saving the SPRN_SPRG3 before entering a deep stop state,
and restoring it back on wakeup from the stop state.

Reported-by: Florian Weimer <fweimer@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/cpuidle.h | 1 +
 arch/powerpc/kernel/asm-offsets.c  | 1 +
 arch/powerpc/kernel/idle_book3s.S  | 5 +++++
 3 files changed, 7 insertions(+)

diff --git a/arch/powerpc/include/asm/cpuidle.h b/arch/powerpc/include/asm/cpuidle.h
index e210a83..03fa904 100644
--- a/arch/powerpc/include/asm/cpuidle.h
+++ b/arch/powerpc/include/asm/cpuidle.h
@@ -77,6 +77,7 @@ struct stop_sprs {
 	u64 mmcr1;
 	u64 mmcr2;
 	u64 mmcra;
+	u64 sprg3;
 };
 
 extern u32 pnv_fastsleep_workaround_at_entry[];
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 89cf155..a35ebfc 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -776,6 +776,7 @@ int main(void)
 	STOP_SPR(STOP_MMCR1, mmcr1);
 	STOP_SPR(STOP_MMCR2, mmcr2);
 	STOP_SPR(STOP_MMCRA, mmcra);
+	STOP_SPR(STOP_SPRG3, sprg3);
 #endif
 
 	DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER);
diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index d85d551..5069d42 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -120,6 +120,9 @@ power9_save_additional_sprs:
 	mfspr	r4, SPRN_MMCR2
 	std	r3, STOP_MMCR1(r13)
 	std	r4, STOP_MMCR2(r13)
+
+	mfspr	r3, SPRN_SPRG3
+	std	r3, STOP_SPRG3(r13)
 	blr
 
 power9_restore_additional_sprs:
@@ -144,7 +147,9 @@ power9_restore_additional_sprs:
 	mtspr	SPRN_MMCR1, r4
 
 	ld	r3, STOP_MMCR2(r13)
+	ld	r4, STOP_SPRG3(r13)
 	mtspr	SPRN_MMCR2, r3
+	mtspr	SPRN_SPRG3, r4
 	blr
 
 /*
-- 
1.9.4