powerpc/powernv: Restore non-volatile CRs after nap

sambltc · mpe · commit 0aab3747091d · 2015-05-01T16:55:11.000+10:00
Patches 7cba160 "powernv/cpuidle: Redesign idle states management" and 77b54e9 "powernv/powerpc: Add winkle support for offline cpus" use non-volatile condition registers (cr2, cr3 and cr4) early in the system reset interrupt handler (system_reset_pSeries()) before it has been determined if state loss has occurred. If state loss has not occurred, control returns via the power7_wakeup_noloss() path which does not restore those condition registers, leaving them corrupted. Fix this by restoring the condition registers in the power7_wakeup_noloss() case. This is apparent when running a KVM guest on hardware that does not support winkle or sleep and the guest makes use of secondary threads. In practice this means Power7 machines, though some early unreleased Power8 machines may also be susceptible. The secondary CPUs are taken off line before the guest is started and they call pnv_smp_cpu_kill_self(). This checks support for sleep states (in this case there is no support) and power7_nap() is called. When the CPU is woken, power7_nap() returns and because the CPU is still off line, the main while loop executes again. The sleep states support test is executed again, but because the tested values cannot have changed, the compiler has optimized the test away and instead we rely on the result of the first test, which has been left in cr3 and/or cr4. With the result overwritten, the wrong branch is taken and power7_winkle() is called on a CPU that does not support it, leading to it stalling. Fixes: 7cba160 ("powernv/cpuidle: Redesign idle states management") Fixes: 77b54e9 ("powernv/powerpc: Add winkle support for offline cpus") [mpe: Massage change log a bit more] Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/kernel/idle_power7.S b/arch/powerpc/kernel/idle_power7.S
@@ -501,9 +501,11 @@ BEGIN_FTR_SECTION
 	CHECK_HMI_INTERRUPT
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 	ld	r1,PACAR1(r13)
+	ld	r6,_CCR(r1)
 	ld	r4,_MSR(r1)
 	ld	r5,_NIP(r1)
 	addi	r1,r1,INT_FRAME_SIZE
+	mtcr	r6
 	mtspr	SPRN_SRR1,r4
 	mtspr	SPRN_SRR0,r5
 	rfid
