KVM: arm64: Remove host_cpu_context member from vcpu structure

For very long, we have kept this pointer back to the per-cpu
host state, despite having working per-cpu accessors at EL2
for some time now.

Recent investigations have shown that this pointer is easy
to abuse in preemptible context, which is a sure sign that
it would better be gone. Not to mention that a per-cpu
pointer is faster to access at all times.

Reported-by: Andrew Scull <ascull@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com
Reviewed-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_host.h

@@ -284,9 +284,6 @@ struct kvm_vcpu_arch {
 	struct kvm_guest_debug_arch vcpu_debug_state;
 	struct kvm_guest_debug_arch external_debug_state;
 
-	/* Pointer to host CPU context */
-	struct kvm_cpu_context *host_cpu_context;
-
 	struct thread_info *host_thread_info;	/* hyp VA */
 	struct user_fpsimd_state *host_fpsimd_state;	/* hyp VA */
 

arch/arm64/kvm/arm.c

@@ -340,10 +340,8 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	int *last_ran;
-	kvm_host_data_t *cpu_data;
 
 	last_ran = this_cpu_ptr(vcpu->kvm->arch.last_vcpu_ran);
-	cpu_data = this_cpu_ptr(&kvm_host_data);
 
 	/*
 	 * We might get preempted before the vCPU actually runs, but
@@ -355,7 +353,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	}
 
 	vcpu->cpu = cpu;
-	vcpu->arch.host_cpu_context = &cpu_data->host_ctxt;
 
 	kvm_vgic_load(vcpu);
 	kvm_timer_vcpu_load(vcpu);

arch/arm64/kvm/hyp/debug-sr.c

@@ -185,7 +185,7 @@ void __hyp_text __debug_switch_to_guest(struct kvm_vcpu *vcpu)
 	if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
 		return;
 
-	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
+	host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	guest_ctxt = &vcpu->arch.ctxt;
 	host_dbg = &vcpu->arch.host_debug_state.regs;
 	guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr);
@@ -207,7 +207,7 @@ void __hyp_text __debug_switch_to_host(struct kvm_vcpu *vcpu)
 	if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
 		return;
 
-	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
+	host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	guest_ctxt = &vcpu->arch.ctxt;
 	host_dbg = &vcpu->arch.host_debug_state.regs;
 	guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr);

arch/arm64/kvm/hyp/switch.c

@@ -532,7 +532,7 @@ static bool __hyp_text __hyp_handle_ptrauth(struct kvm_vcpu *vcpu)
 	    !esr_is_ptrauth_trap(kvm_vcpu_get_hsr(vcpu)))
 		return false;
 
-	ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
+	ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	__ptrauth_save_key(ctxt->sys_regs, APIA);
 	__ptrauth_save_key(ctxt->sys_regs, APIB);
 	__ptrauth_save_key(ctxt->sys_regs, APDA);
@@ -703,7 +703,7 @@ static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
 	struct kvm_cpu_context *guest_ctxt;
 	u64 exit_code;
 
-	host_ctxt = vcpu->arch.host_cpu_context;
+	host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	host_ctxt->__hyp_running_vcpu = vcpu;
 	guest_ctxt = &vcpu->arch.ctxt;
 
@@ -808,7 +808,7 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
 
 	vcpu = kern_hyp_va(vcpu);
 
-	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
+	host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	host_ctxt->__hyp_running_vcpu = vcpu;
 	guest_ctxt = &vcpu->arch.ctxt;
 

arch/arm64/kvm/hyp/sysreg-sr.c

@@ -265,12 +265,13 @@ void __hyp_text __sysreg32_restore_state(struct kvm_vcpu *vcpu)
  */
 void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
 {
-	struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
 	struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
+	struct kvm_cpu_context *host_ctxt;
 
 	if (!has_vhe())
 		return;
 
+	host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	__sysreg_save_user_state(host_ctxt);
 
 	/*
@@ -301,12 +302,13 @@ void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
  */
 void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
 {
-	struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
 	struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
+	struct kvm_cpu_context *host_ctxt;
 
 	if (!has_vhe())
 		return;
 
+	host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
 	deactivate_traps_vhe_put();
 
 	__sysreg_save_el1_state(guest_ctxt);

arch/arm64/kvm/pmu.c

@@ -163,15 +163,13 @@ static void kvm_vcpu_pmu_disable_el0(unsigned long events)
  */
 void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
 {
-	struct kvm_cpu_context *host_ctxt;
 	struct kvm_host_data *host;
 	u32 events_guest, events_host;
 
 	if (!has_vhe())
 		return;
 
-	host_ctxt = vcpu->arch.host_cpu_context;
+	host = this_cpu_ptr(&kvm_host_data);
-	host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
 	events_guest = host->pmu_events.events_guest;
 	events_host = host->pmu_events.events_host;
 
@@ -184,15 +182,13 @@ void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
  */
 void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu)
 {
-	struct kvm_cpu_context *host_ctxt;
 	struct kvm_host_data *host;
 	u32 events_guest, events_host;
 
 	if (!has_vhe())
 		return;
 
-	host_ctxt = vcpu->arch.host_cpu_context;
+	host = this_cpu_ptr(&kvm_host_data);
-	host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
 	events_guest = host->pmu_events.events_guest;
 	events_host = host->pmu_events.events_host;