KVM: PPC: Book3S HV: Handle unexpected interrupts better

At present, if an interrupt (i.e. an exception or trap) occurs in the
code where KVM is switching the MMU to or from guest context, we jump
to kvmppc_bad_host_intr, where we simply spin with interrupts disabled.
In this situation, it is hard to debug what happened because we get no
indication as to which interrupt occurred or where.  Typically we get
a cascade of stall and soft lockup warnings from other CPUs.

In order to get more information for debugging, this adds code to
create a stack frame on the emergency stack and save register values
to it.  We start half-way down the emergency stack in order to give
ourselves some chance of being able to do a stack trace on secondary
threads that are already on the emergency stack.

On POWER7 or POWER8, we then just spin, as before, because we don't
know what state the MMU context is in or what other threads are doing,
and we can't switch back to host context without coordinating with
other threads.  On POWER9 we can do better; there we load up the host
MMU context and jump to C code, which prints an oops message to the
console and panics.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_hv_builtin.c

@@ -601,3 +601,9 @@ int kvmppc_rm_h_eoi(struct kvm_vcpu *vcpu, unsigned long xirr)
 		return xics_rm_h_eoi(vcpu, xirr);
 }
 #endif /* CONFIG_KVM_XICS */
+
+void kvmppc_bad_interrupt(struct pt_regs *regs)
+{
+	die("Bad interrupt in KVM entry/exit code", regs, SIGABRT);
+	panic("Bad KVM trap");
+}

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -31,6 +31,7 @@
 #include <asm/tm.h>
 #include <asm/opal.h>
 #include <asm/xive-regs.h>
+#include <asm/thread_info.h>
 
 /* Sign-extend HDEC if not on POWER9 */
 #define EXTEND_HDEC(reg)			\
@@ -3134,10 +3135,139 @@ kvmppc_restore_tm:
 /*
  * We come here if we get any exception or interrupt while we are
  * executing host real mode code while in guest MMU context.
- * For now just spin, but we should do something better.
+ * r12 is (CR << 32) | vector
+ * r13 points to our PACA
+ * r12 is saved in HSTATE_SCRATCH0(r13)
+ * ctr is saved in HSTATE_SCRATCH1(r13) if RELOCATABLE
+ * r9 is saved in HSTATE_SCRATCH2(r13)
+ * r13 is saved in HSPRG1
+ * cfar is saved in HSTATE_CFAR(r13)
+ * ppr is saved in HSTATE_PPR(r13)
  */
 kvmppc_bad_host_intr:
+	/*
+	 * Switch to the emergency stack, but start half-way down in
+	 * case we were already on it.
+	 */
+	mr	r9, r1
+	std	r1, PACAR1(r13)
+	ld	r1, PACAEMERGSP(r13)
+	subi	r1, r1, THREAD_SIZE/2 + INT_FRAME_SIZE
+	std	r9, 0(r1)
+	std	r0, GPR0(r1)
+	std	r9, GPR1(r1)
+	std	r2, GPR2(r1)
+	SAVE_4GPRS(3, r1)
+	SAVE_2GPRS(7, r1)
+	srdi	r0, r12, 32
+	clrldi	r12, r12, 32
+	std	r0, _CCR(r1)
+	std	r12, _TRAP(r1)
+	andi.	r0, r12, 2
+	beq	1f
+	mfspr	r3, SPRN_HSRR0
+	mfspr	r4, SPRN_HSRR1
+	mfspr	r5, SPRN_HDAR
+	mfspr	r6, SPRN_HDSISR
+	b	2f
+1:	mfspr	r3, SPRN_SRR0
+	mfspr	r4, SPRN_SRR1
+	mfspr	r5, SPRN_DAR
+	mfspr	r6, SPRN_DSISR
+2:	std	r3, _NIP(r1)
+	std	r4, _MSR(r1)
+	std	r5, _DAR(r1)
+	std	r6, _DSISR(r1)
+	ld	r9, HSTATE_SCRATCH2(r13)
+	ld	r12, HSTATE_SCRATCH0(r13)
+	GET_SCRATCH0(r0)
+	SAVE_4GPRS(9, r1)
+	std	r0, GPR13(r1)
+	SAVE_NVGPRS(r1)
+	ld	r5, HSTATE_CFAR(r13)
+	std	r5, ORIG_GPR3(r1)
+	mflr	r3
+#ifdef CONFIG_RELOCATABLE
+	ld	r4, HSTATE_SCRATCH1(r13)
+#else
+	mfctr	r4
+#endif
+	mfxer	r5
+	lbz	r6, PACASOFTIRQEN(r13)
+	std	r3, _LINK(r1)
+	std	r4, _CTR(r1)
+	std	r5, _XER(r1)
+	std	r6, SOFTE(r1)
+	ld	r2, PACATOC(r13)
+	LOAD_REG_IMMEDIATE(3, 0x7265677368657265)
+	std	r3, STACK_FRAME_OVERHEAD-16(r1)
+
+	/*
+	 * On POWER9 do a minimal restore of the MMU and call C code,
+	 * which will print a message and panic.
+	 * XXX On POWER7 and POWER8, we just spin here since we don't
+	 * know what the other threads are doing (and we don't want to
+	 * coordinate with them) - but at least we now have register state
+	 * in memory that we might be able to look at from another CPU.
+	 */
+BEGIN_FTR_SECTION
 	b	.
+END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
+	ld	r9, HSTATE_KVM_VCPU(r13)
+	ld	r10, VCPU_KVM(r9)
+
+	li	r0, 0
+	mtspr	SPRN_AMR, r0
+	mtspr	SPRN_IAMR, r0
+	mtspr	SPRN_CIABR, r0
+	mtspr	SPRN_DAWRX, r0
+
+	/* Flush the ERAT on radix P9 DD1 guest exit */
+BEGIN_FTR_SECTION
+	PPC_INVALIDATE_ERAT
+END_FTR_SECTION_IFSET(CPU_FTR_POWER9_DD1)
+
+BEGIN_MMU_FTR_SECTION
+	b	4f
+END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
+
+	slbmte	r0, r0
+	slbia
+	ptesync
+	ld	r8, PACA_SLBSHADOWPTR(r13)
+	.rept	SLB_NUM_BOLTED
+	li	r3, SLBSHADOW_SAVEAREA
+	LDX_BE	r5, r8, r3
+	addi	r3, r3, 8
+	LDX_BE	r6, r8, r3
+	andis.	r7, r5, SLB_ESID_V@h
+	beq	3f
+	slbmte	r6, r5
+3:	addi	r8, r8, 16
+	.endr
+
+4:	lwz	r7, KVM_HOST_LPID(r10)
+	mtspr	SPRN_LPID, r7
+	mtspr	SPRN_PID, r0
+	ld	r8, KVM_HOST_LPCR(r10)
+	mtspr	SPRN_LPCR, r8
+	isync
+	li	r0, KVM_GUEST_MODE_NONE
+	stb	r0, HSTATE_IN_GUEST(r13)
+
+	/*
+	 * Turn on the MMU and jump to C code
+	 */
+	bcl	20, 31, .+4
+5:	mflr	r3
+	addi	r3, r3, 9f - 5b
+	ld	r4, PACAKMSR(r13)
+	mtspr	SPRN_SRR0, r3
+	mtspr	SPRN_SRR1, r4
+	rfid
+9:	addi	r3, r1, STACK_FRAME_OVERHEAD
+	bl	kvmppc_bad_interrupt
+	b	9b
 
 /*
  * This mimics the MSR transition on IRQ delivery.  The new guest MSR is taken