KVM: PPC: Book3S PR: Cope with doorbell interrupts

When the PR host is running on a POWER8 machine in POWER8 mode, it
will use doorbell interrupts for IPIs.  If one of them arrives while
we are in the guest, we pop out of the guest with trap number 0xA00,
which isn't handled by kvmppc_handle_exit_pr, leading to the following
BUG_ON:

[  331.436215] exit_nr=0xa00 | pc=0x1d2c | msr=0x800000000000d032
[  331.437522] ------------[ cut here ]------------
[  331.438296] kernel BUG at arch/powerpc/kvm/book3s_pr.c:982!
[  331.439063] Oops: Exception in kernel mode, sig: 5 [#2]
[  331.439819] SMP NR_CPUS=1024 NUMA pSeries
[  331.440552] Modules linked in: tun nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw virtio_net kvm binfmt_misc ibmvscsi scsi_transport_srp scsi_tgt virtio_blk
[  331.447614] CPU: 11 PID: 1296 Comm: qemu-system-ppc Tainted: G      D      3.11.7-200.2.fc19.ppc64p7 #1
[  331.448920] task: c0000003bdc8c000 ti: c0000003bd32c000 task.ti: c0000003bd32c000
[  331.450088] NIP: d0000000025d6b9c LR: d0000000025d6b98 CTR: c0000000004cfdd0
[  331.451042] REGS: c0000003bd32f420 TRAP: 0700   Tainted: G      D       (3.11.7-200.2.fc19.ppc64p7)
[  331.452331] MSR: 800000000282b032 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI>  CR: 28004824  XER: 20000000
[  331.454616] SOFTE: 1
[  331.455106] CFAR: c000000000848bb8
[  331.455726]
GPR00: d0000000025d6b98 c0000003bd32f6a0 d0000000026017b8 0000000000000032
GPR04: c0000000018627f8 c000000001873208 320d0a3030303030 3030303030643033
GPR08: c000000000c490a8 0000000000000000 0000000000000000 0000000000000002
GPR12: 0000000028004822 c00000000fdc6300 0000000000000000 00000100076ec310
GPR16: 000000002ae343b8 00003ffffd397398 0000000000000000 0000000000000000
GPR20: 00000100076f16f4 00000100076ebe60 0000000000000008 ffffffffffffffff
GPR24: 0000000000000000 0000008001041e60 0000000000000000 0000008001040ce8
GPR28: c0000003a2d80000 0000000000000a00 0000000000000001 c0000003a2681810
[  331.466504] NIP [d0000000025d6b9c] .kvmppc_handle_exit_pr+0x75c/0xa80 [kvm]
[  331.466999] LR [d0000000025d6b98] .kvmppc_handle_exit_pr+0x758/0xa80 [kvm]
[  331.467517] Call Trace:
[  331.467909] [c0000003bd32f6a0] [d0000000025d6b98] .kvmppc_handle_exit_pr+0x758/0xa80 [kvm] (unreliable)
[  331.468553] [c0000003bd32f750] [d0000000025d98f0] kvm_start_lightweight+0xb4/0xc4 [kvm]
[  331.469189] [c0000003bd32f920] [d0000000025d7648] .kvmppc_vcpu_run_pr+0xd8/0x270 [kvm]
[  331.469838] [c0000003bd32f9c0] [d0000000025cf748] .kvmppc_vcpu_run+0xc8/0xf0 [kvm]
[  331.470790] [c0000003bd32fa50] [d0000000025cc19c] .kvm_arch_vcpu_ioctl_run+0x5c/0x1b0 [kvm]
[  331.471401] [c0000003bd32fae0] [d0000000025c4888] .kvm_vcpu_ioctl+0x478/0x730 [kvm]
[  331.472026] [c0000003bd32fc90] [c00000000026192c] .do_vfs_ioctl+0x4dc/0x7a0
[  331.472561] [c0000003bd32fd80] [c000000000261cc4] .SyS_ioctl+0xd4/0xf0
[  331.473095] [c0000003bd32fe30] [c000000000009ed8] syscall_exit+0x0/0x98
[  331.473633] Instruction dump:
[  331.473766] 4bfff9b4 2b9d0800 419efc18 60000000 60420000 3d220000 e8bf11a0 e8df12a8
[  331.474733] 7fa4eb78 e8698660 48015165 e8410028 <0fe00000> 813f00e4 3ba00000 39290001
[  331.475386] ---[ end trace 49fc47d994c1f8f2 ]---
[  331.479817]

This fixes the problem by making kvmppc_handle_exit_pr() recognize the
interrupt.  We also need to jump to the doorbell interrupt handler in
book3s_segment.S to handle the interrupt on the way out of the guest.
Having done that, there's nothing further to be done in
kvmppc_handle_exit_pr().
Signed-off-by: NPaul Mackerras <paulus@samba.org>
Signed-off-by: NAlexander Graf <agraf@suse.de>

arch/powerpc/include/asm/kvm_asm.h

@@ -91,6 +91,7 @@
 #define BOOK3S_INTERRUPT_FP_UNAVAIL	0x800
 #define BOOK3S_INTERRUPT_DECREMENTER	0x900
 #define BOOK3S_INTERRUPT_HV_DECREMENTER	0x980
+#define BOOK3S_INTERRUPT_DOORBELL	0xa00
 #define BOOK3S_INTERRUPT_SYSCALL	0xc00
 #define BOOK3S_INTERRUPT_TRACE		0xd00
 #define BOOK3S_INTERRUPT_H_DATA_STORAGE	0xe00

arch/powerpc/kvm/book3s_pr.c

@@ -827,6 +827,7 @@ int kvmppc_handle_exit_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	/* We're good on these - the host merely wanted to get our attention */
 	case BOOK3S_INTERRUPT_DECREMENTER:
 	case BOOK3S_INTERRUPT_HV_DECREMENTER:
+	case BOOK3S_INTERRUPT_DOORBELL:
 		vcpu->stat.dec_exits++;
 		r = RESUME_GUEST;
 		break;

arch/powerpc/kvm/book3s_segment.S

@@ -361,6 +361,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 	beqa	BOOK3S_INTERRUPT_DECREMENTER
 	cmpwi	r12, BOOK3S_INTERRUPT_PERFMON
 	beqa	BOOK3S_INTERRUPT_PERFMON
+	cmpwi	r12, BOOK3S_INTERRUPT_DOORBELL
+	beqa	BOOK3S_INTERRUPT_DOORBELL
 
 	RFI
 kvmppc_handler_trampoline_exit_end: