[RFC/PATCH 1/3] powerpc/kvm: Handle H_FAC_UNAVAIL when guest executes stop.

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

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

If a guest executes a stop instruction when the hypervisor has set the
PSSCR[ESL|EC] bits, the processor will throw an Hypervisor Facility
Unavailable exception. Currently when we receive this exception, we
only check if the exeception is generated due to a doorbell
instruction, in which case we emulate it. For all other cases,
including the case when the guest executes a stop-instruction, the
hypervisor sends a PROGILL to the guest program, which results in a
guest crash.

This patch adds code to handle the case when the hypervisor receives a
H_FAC_UNAVAIL exception due to guest executing the stop
instruction. The hypervisor increments the pc to the next instruction
and resumes the guest as expected by the semantics of the
PSSCR[ESL|EC] = 0 stop instruction.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/reg.h | 1 +
 arch/powerpc/kvm/book3s_hv.c   | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index da5cab0..2568c18 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -399,6 +399,7 @@
 /* HFSCR and FSCR bit numbers are the same */
 #define FSCR_SCV_LG	12	/* Enable System Call Vectored */
 #define FSCR_MSGP_LG	10	/* Enable MSGP */
+#define FSCR_STOP_LG    9       /* Enable stop states */
 #define FSCR_TAR_LG	8	/* Enable Target Address Register */
 #define FSCR_EBB_LG	7	/* Enable Event Based Branching */
 #define FSCR_TM_LG	5	/* Enable Transactional Memory */
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 33be4d9..cdb7224 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1419,7 +1419,11 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		if (((vcpu->arch.hfscr >> 56) == FSCR_MSGP_LG) &&
 		    cpu_has_feature(CPU_FTR_ARCH_300))
 			r = kvmppc_emulate_doorbell_instr(vcpu);
-		if (r == EMULATE_FAIL) {
+		else if (((vcpu->arch.hfscr >> 56) == FSCR_STOP_LG) &&
+			cpu_has_feature(CPU_FTR_ARCH_300)) {
+			kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) + 4);
+			r = RESUME_GUEST;
+		} else if (r == EMULATE_FAIL) {
 			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
 			r = RESUME_GUEST;
 		}
-- 
1.9.4