arm/arm64: KVM: Allow a VCPU to fully reset itself

The current kvm_psci_vcpu_on implementation will directly try to
manipulate the state of the VCPU to reset it.  However, since this is
not done on the thread that runs the VCPU, we can end up in a strangely
corrupted state when the source and target VCPUs are running at the same
time.

Fix this by factoring out all reset logic from the PSCI implementation
and forwarding the required information along with a request to the
target VCPU.

Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index ca56537b61bc..50e89869178a 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -48,6 +48,7 @@
 #define KVM_REQ_SLEEP \
 	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_IRQ_PENDING	KVM_ARCH_REQ(1)
+#define KVM_REQ_VCPU_RESET	KVM_ARCH_REQ(2)
 
 DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
 
@@ -147,6 +148,13 @@ struct kvm_cpu_context {
 
 typedef struct kvm_cpu_context kvm_cpu_context_t;
 
+struct vcpu_reset_state {
+	unsigned long	pc;
+	unsigned long	r0;
+	bool		be;
+	bool		reset;
+};
+
 struct kvm_vcpu_arch {
 	struct kvm_cpu_context ctxt;
 
@@ -186,6 +194,8 @@ struct kvm_vcpu_arch {
 	/* Cache some mmu pages needed inside spinlock regions */
 	struct kvm_mmu_memory_cache mmu_page_cache;
 
+	struct vcpu_reset_state reset_state;
+
 	/* Detect first run of a vcpu */
 	bool has_run_once;
 };
diff --git a/arch/arm/kvm/reset.c b/arch/arm/kvm/reset.c
index 5ed0c3ee33d6..e53327912adc 100644
--- a/arch/arm/kvm/reset.c
+++ b/arch/arm/kvm/reset.c
@@ -26,6 +26,7 @@
 #include <asm/cputype.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_coproc.h>
+#include <asm/kvm_emulate.h>
 
 #include <kvm/arm_arch_timer.h>
 
@@ -69,6 +70,29 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	/* Reset CP15 registers */
 	kvm_reset_coprocs(vcpu);
 
+	/*
+	 * Additional reset state handling that PSCI may have imposed on us.
+	 * Must be done after all the sys_reg reset.
+	 */
+	if (READ_ONCE(vcpu->arch.reset_state.reset)) {
+		unsigned long target_pc = vcpu->arch.reset_state.pc;
+
+		/* Gracefully handle Thumb2 entry point */
+		if (target_pc & 1) {
+			target_pc &= ~1UL;
+			vcpu_set_thumb(vcpu);
+		}
+
+		/* Propagate caller endianness */
+		if (vcpu->arch.reset_state.be)
+			kvm_vcpu_set_be(vcpu);
+
+		*vcpu_pc(vcpu) = target_pc;
+		vcpu_set_reg(vcpu, 0, vcpu->arch.reset_state.r0);
+
+		vcpu->arch.reset_state.reset = false;
+	}
+
 	/* Reset arch_timer context */
 	return kvm_timer_vcpu_reset(vcpu);
 }