KVM: arm64: nv: Plumb handling of GICv3 EL2 accesses

Wire the handling of all GICv3 EL2 registers, and provide emulation
for all the non memory-backed registers (ICC_SRE_EL2, ICH_VTR_EL2,
ICH_MISR_EL2, ICH_ELRSR_EL2, and ICH_EISR_EL2).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250225172930.1850838-7-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

1 files changed, 125 insertions, 0 deletions

diff --git a/arch/arm64/kvm/vgic/vgic-v3-nested.c b/arch/arm64/kvm/vgic/vgic-v3-nested.c
new file mode 100644
index 000000000000..48bfd2f556a3
--- /dev/null
+++ b/arch/arm64/kvm/vgic/vgic-v3-nested.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/cpu.h>
+#include <linux/kvm.h>
+#include <linux/kvm_host.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/uaccess.h>
+
+#include <kvm/arm_vgic.h>
+
+#include <asm/kvm_arm.h>
+#include <asm/kvm_emulate.h>
+#include <asm/kvm_nested.h>
+
+#include "vgic.h"
+
+#define ICH_LRN(n)	(ICH_LR0_EL2 + (n))
+
+struct mi_state {
+	u16	eisr;
+	u16	elrsr;
+	bool	pend;
+};
+
+/*
+ * Nesting GICv3 support
+ *
+ * System register emulation:
+ *
+ * We get two classes of registers:
+ *
+ * - those backed by memory (LRs, APRs, HCR, VMCR): L1 can freely access
+ *   them, and L0 doesn't see a thing.
+ *
+ * - those that always trap (ELRSR, EISR, MISR): these are status registers
+ *   that are built on the fly based on the in-memory state.
+ *
+ * Only L1 can access the ICH_*_EL2 registers. A non-NV L2 obviously cannot,
+ * and a NV L2 would either access the VNCR page provided by L1 (memory
+ * based registers), or see the access redirected to L1 (registers that
+ * trap) thanks to NV being set by L1.
+ */
+
+static bool lr_triggers_eoi(u64 lr)
+{
+	return !(lr & (ICH_LR_STATE | ICH_LR_HW)) && (lr & ICH_LR_EOI);
+}
+
+static void vgic_compute_mi_state(struct kvm_vcpu *vcpu, struct mi_state *mi_state)
+{
+	u16 eisr = 0, elrsr = 0;
+	bool pend = false;
+
+	for (int i = 0; i < kvm_vgic_global_state.nr_lr; i++) {
+		u64 lr = __vcpu_sys_reg(vcpu, ICH_LRN(i));
+
+		if (lr_triggers_eoi(lr))
+			eisr |= BIT(i);
+		if (!(lr & ICH_LR_STATE))
+			elrsr |= BIT(i);
+		pend |= (lr & ICH_LR_PENDING_BIT);
+	}
+
+	mi_state->eisr	= eisr;
+	mi_state->elrsr	= elrsr;
+	mi_state->pend	= pend;
+}
+
+u16 vgic_v3_get_eisr(struct kvm_vcpu *vcpu)
+{
+	struct mi_state mi_state;
+
+	vgic_compute_mi_state(vcpu, &mi_state);
+	return mi_state.eisr;
+}
+
+u16 vgic_v3_get_elrsr(struct kvm_vcpu *vcpu)
+{
+	struct mi_state mi_state;
+
+	vgic_compute_mi_state(vcpu, &mi_state);
+	return mi_state.elrsr;
+}
+
+u64 vgic_v3_get_misr(struct kvm_vcpu *vcpu)
+{
+	struct mi_state mi_state;
+	u64 reg = 0, hcr, vmcr;
+
+	hcr = __vcpu_sys_reg(vcpu, ICH_HCR_EL2);
+	vmcr = __vcpu_sys_reg(vcpu, ICH_VMCR_EL2);
+
+	vgic_compute_mi_state(vcpu, &mi_state);
+
+	if (mi_state.eisr)
+		reg |= ICH_MISR_EL2_EOI;
+
+	if (__vcpu_sys_reg(vcpu, ICH_HCR_EL2) & ICH_HCR_EL2_UIE) {
+		int used_lrs = kvm_vgic_global_state.nr_lr;
+
+		used_lrs -= hweight16(mi_state.elrsr);
+		reg |= (used_lrs <= 1) ? ICH_MISR_EL2_U : 0;
+	}
+
+	if ((hcr & ICH_HCR_EL2_LRENPIE) && FIELD_GET(ICH_HCR_EL2_EOIcount_MASK, hcr))
+		reg |= ICH_MISR_EL2_LRENP;
+
+	if ((hcr & ICH_HCR_EL2_NPIE) && !mi_state.pend)
+		reg |= ICH_MISR_EL2_NP;
+
+	if ((hcr & ICH_HCR_EL2_VGrp0EIE) && (vmcr & ICH_VMCR_ENG0_MASK))
+		reg |= ICH_MISR_EL2_VGrp0E;
+
+	if ((hcr & ICH_HCR_EL2_VGrp0DIE) && !(vmcr & ICH_VMCR_ENG0_MASK))
+		reg |= ICH_MISR_EL2_VGrp0D;
+
+	if ((hcr & ICH_HCR_EL2_VGrp1EIE) && (vmcr & ICH_VMCR_ENG1_MASK))
+		reg |= ICH_MISR_EL2_VGrp1E;
+
+	if ((hcr & ICH_HCR_EL2_VGrp1DIE) && !(vmcr & ICH_VMCR_ENG1_MASK))
+		reg |= ICH_MISR_EL2_VGrp1D;
+
+	return reg;
+}