[RFC PATCH v1 5/6] KVM: s390: Give BUSY to SIGP SENSE during Restart

[Eric Farman <farman@linux.ibm.com>]

A SIGP RESTART is a special animal, in that it directs the
destination CPU to perform the restart operation. This is
basically the loading of the Restart PSW and letting it take
over, but a stopped CPU must first be made operating for this
to work correctly.

As this can take a moment, let's leave a reminder that this
SIGP is being processed, such that the SIGP SENSE logic
(which is not handled in userspace) can return CC=2 instead
of CC=1 (and STOPPED) until the CPU is started.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h |  1 +
 arch/s390/kvm/kvm-s390.c         |  1 +
 arch/s390/kvm/sigp.c             | 17 +++++++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index a604d51acfc8..536f174c5e81 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -746,6 +746,7 @@ struct kvm_vcpu_arch {
 	__u64 cputm_start;
 	bool gs_enabled;
 	bool skey_enabled;
+	bool sigp_restart;
 	struct kvm_s390_pv_vcpu pv;
 	union diag318_info diag318_info;
 };
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6a6dd5e1daf6..33d71fa42d68 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4603,6 +4603,7 @@ int kvm_s390_vcpu_start(struct kvm_vcpu *vcpu)
 	}
 
 	kvm_s390_clear_cpuflags(vcpu, CPUSTAT_STOPPED);
+	vcpu->arch.sigp_restart = 0;
 	/*
 	 * The real PSW might have changed due to a RESTART interpreted by the
 	 * ultravisor. We block all interrupts and let the next sie exit
diff --git a/arch/s390/kvm/sigp.c b/arch/s390/kvm/sigp.c
index c64e37f4347d..5a21354d0265 100644
--- a/arch/s390/kvm/sigp.c
+++ b/arch/s390/kvm/sigp.c
@@ -27,6 +27,8 @@ static int __sigp_sense(struct kvm_vcpu *vcpu, struct kvm_vcpu *dst_vcpu,
 	ext_call_pending = kvm_s390_ext_call_pending(dst_vcpu);
 	if (!stopped && !ext_call_pending)
 		rc = SIGP_CC_ORDER_CODE_ACCEPTED;
+	else if (stopped && dst_vcpu->arch.sigp_restart)
+		rc = SIGP_CC_BUSY;
 	else {
 		*reg &= 0xffffffff00000000UL;
 		if (ext_call_pending)
@@ -385,6 +387,18 @@ static int handle_sigp_order_in_user_space(struct kvm_vcpu *vcpu, u8 order_code,
 	return 1;
 }
 
+static void handle_sigp_restart(struct kvm_vcpu *vcpu, u16 cpu_addr)
+{
+	struct kvm_vcpu *dst_vcpu = kvm_get_vcpu_by_id(vcpu->kvm, cpu_addr);
+
+	/* Ignore SIGP Restart to non-existent CPUs */
+	if (!dst_vcpu)
+		return;
+
+	if (is_vcpu_stopped(dst_vcpu))
+		dst_vcpu->arch.sigp_restart = 1;
+}
+
 static int handle_sigp_order_is_blocked(struct kvm_vcpu *vcpu, u8 order_code,
 					u16 cpu_addr)
 {
@@ -443,6 +457,9 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu)
 	if (handle_sigp_order_is_blocked(vcpu, order_code, cpu_addr))
 		return 0;
 
+	if (order_code == SIGP_RESTART)
+		handle_sigp_restart(vcpu, cpu_addr);
+
 	if (handle_sigp_order_in_user_space(vcpu, order_code, cpu_addr))
 		return -EOPNOTSUPP;
 
-- 
2.25.1