[PATCH 15/16] KVM: arm64: nv: Fold GICv3 host trapping requirements into guest setup

Marc Zyngier
2024-12-17T15:14:07Z

Popular HW that is able to use NV also has a broken vgic implementation
that requires trapping.

On such HW, propagate the host trap bits into the guest's shadow
ICH_HCR_EL2 register, making sure we don't allow an L2 guest to bring
the system down.

This involves a bit of tweaking so that the emulation code correctly
poicks up the shadow state as needed, and to only partially sync
ICH_HCR_EL2 back with the guest state to capture EOIcount.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/vgic/vgic-v3-nested.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-v3-nested.c b/arch/arm64/kvm/vgic/vgic-v3-nested.c
index b81bfa85ebb19..778ffb62de21c 100644
--- a/arch/arm64/kvm/vgic/vgic-v3-nested.c
+++ b/arch/arm64/kvm/vgic/vgic-v3-nested.c
@@ -296,9 +296,19 @@ static void vgic_v3_create_shadow_state(struct kvm_vcpu *vcpu,
struct vgic_v3_cpu_if *s_cpu_if)
{
struct vgic_v3_cpu_if *host_if = &vcpu->arch.vgic_cpu.vgic_v3;
+ u64 val = 0;
int i;

- s_cpu_if->vgic_hcr = __vcpu_sys_reg(vcpu, ICH_HCR_EL2);
+ /*
+ * If we're on a system with a broken vgic that requires
+ * trapping, propagate the trapping requirements.
+ *
+ * Ah, the smell of rotten fruits...
+ */
+ if (static_branch_unlikely(&vgic_v3_cpuif_trap))
+ val = host_if->vgic_hcr & (ICH_HCR_EL2_TALL0 | ICH_HCR_EL2_TALL1 |
+ ICH_HCR_EL2_TC | ICH_HCR_EL2_TDIR);
+ s_cpu_if->vgic_hcr = __vcpu_sys_reg(vcpu, ICH_HCR_EL2) | val;
s_cpu_if->vgic_vmcr = __vcpu_sys_reg(vcpu, ICH_VMCR_EL2);
s_cpu_if->vgic_sre = host_if->vgic_sre;

@@ -335,6 +345,7 @@ void vgic_v3_put_nested(struct kvm_vcpu *vcpu)
{
struct shadow_if *shadow_if = get_shadow_if();
struct vgic_v3_cpu_if *s_cpu_if = &shadow_if->cpuif;
+ u64 val;
int i;

__vgic_v3_save_vmcr_aprs(s_cpu_if);
@@ -345,7 +356,10 @@ void vgic_v3_put_nested(struct kvm_vcpu *vcpu)
* Translate the shadow state HW fields back to the virtual ones
* before copying the shadow struct back to the nested one.
*/
- __vcpu_sys_reg(vcpu, ICH_HCR_EL2) = s_cpu_if->vgic_hcr;
+ val = __vcpu_sys_reg(vcpu, ICH_HCR_EL2);
+ val &= ~ICH_HCR_EL2_EOIcount_MASK;
+ val |= (s_cpu_if->vgic_hcr & ICH_HCR_EL2_EOIcount_MASK);
+ __vcpu_sys_reg(vcpu, ICH_HCR_EL2) = val;
__vcpu_sys_reg(vcpu, ICH_VMCR_EL2) = s_cpu_if->vgic_vmcr;

for (i = 0; i < 4; i++) {
@@ -354,7 +368,7 @@ void vgic_v3_put_nested(struct kvm_vcpu *vcpu)
}

for_each_set_bit(i, &shadow_if->lr_map, kvm_vgic_global_state.nr_lr) {
- u64 val = __vcpu_sys_reg(vcpu, ICH_LRN(i));
+ val = __vcpu_sys_reg(vcpu, ICH_LRN(i));

val &= ~ICH_LR_STATE;
val |= s_cpu_if->vgic_lr[i] & ICH_LR_STATE;
--
2.39.2