arm64: kvm: Unmask PMR before entering guest

Interrupts masked by ICC_PMR_EL1 will not be signaled to the CPU. This
means that hypervisor will not receive masked interrupts while running a
guest.

We need to make sure that all maskable interrupts are masked from the
time we call local_irq_disable() in the main run loop, and remain so
until we call local_irq_enable() after returning from the guest, and we
need to ensure that we see no interrupts at all (including pseudo-NMIs)
in the middle of the VM world-switch, while at the same time we need to
ensure we exit the guest when there are interrupts for the host.

We can accomplish this with pseudo-NMIs enabled by:
  (1) local_irq_disable: set the priority mask
  (2) enter guest: set PSTATE.I
  (3)              clear the priority mask
  (4) eret to guest
  (5) exit guest:  set the priotiy mask
                   clear PSTATE.I (and restore other host PSTATE bits)
  (6) local_irq_enable: clear the priority mask.
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/kvm_host.h

@@ -24,6 +24,7 @@
 
 #include <linux/types.h>
 #include <linux/kvm_types.h>
+#include <asm/arch_gicv3.h>
 #include <asm/cpufeature.h>
 #include <asm/daifflags.h>
 #include <asm/fpsimd.h>
@@ -474,10 +475,25 @@ static inline int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
 static inline void kvm_arm_vhe_guest_enter(void)
 {
 	local_daif_mask();
+
+	/*
+	 * Having IRQs masked via PMR when entering the guest means the GIC
+	 * will not signal the CPU of interrupts of lower priority, and the
+	 * only way to get out will be via guest exceptions.
+	 * Naturally, we want to avoid this.
+	 */
+	if (system_uses_irq_prio_masking()) {
+		gic_write_pmr(GIC_PRIO_IRQON);
+		dsb(sy);
+	}
 }
 
 static inline void kvm_arm_vhe_guest_exit(void)
 {
+	/*
+	 * local_daif_restore() takes care to properly restore PSTATE.DAIF
+	 * and the GIC PMR if the host is using IRQ priorities.
+	 */
 	local_daif_restore(DAIF_PROCCTX_NOIRQ);
 
 	/*

arch/arm64/kvm/hyp/switch.c

@@ -22,6 +22,7 @@
 
 #include <kvm/arm_psci.h>
 
+#include <asm/arch_gicv3.h>
 #include <asm/cpufeature.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
@@ -521,6 +522,17 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
 	struct kvm_cpu_context *guest_ctxt;
 	u64 exit_code;
 
+	/*
+	 * Having IRQs masked via PMR when entering the guest means the GIC
+	 * will not signal the CPU of interrupts of lower priority, and the
+	 * only way to get out will be via guest exceptions.
+	 * Naturally, we want to avoid this.
+	 */
+	if (system_uses_irq_prio_masking()) {
+		gic_write_pmr(GIC_PRIO_IRQON);
+		dsb(sy);
+	}
+
 	vcpu = kern_hyp_va(vcpu);
 
 	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
@@ -573,6 +585,10 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
 	 */
 	__debug_switch_to_host(vcpu);
 
+	/* Returning to host will clear PSR.I, remask PMR if needed */
+	if (system_uses_irq_prio_masking())
+		gic_write_pmr(GIC_PRIO_IRQOFF);
+
 	return exit_code;
 }