[PATCH 12/14] KVM: arm64: nv: Program host's VNCR_EL2 to the fixmap address

Marc Zyngier
2025-02-15T15:02:04Z

Since we now have a way to map the guest's VNCR_EL2 on the host,
we can point the host's VNCR_EL2 to it and go full circle!

Note that we unconditionally assign the fixmap to VNCR_EL2,
irrespective of the guest's version being mapped or not. We want
to take a fault on first access, so the fixmap either contains
something guranteed to be either invalid or a guest mapping.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/hyp/vhe/switch.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index 3453fb76cf0e3..6242ab037bfdf 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -48,6 +48,7 @@ DEFINE_PER_CPU(unsigned long, kvm_hyp_vector);

static u64 __compute_hcr(struct kvm_vcpu *vcpu)
{
+ u64 guest_hcr = __vcpu_sys_reg(vcpu, HCR_EL2);
u64 hcr = vcpu->arch.hcr_el2;

if (!vcpu_has_nv(vcpu))
@@ -70,9 +71,23 @@ static u64 __compute_hcr(struct kvm_vcpu *vcpu)
write_sysreg_s(vcpu->arch.ctxt.vncr_array, SYS_VNCR_EL2);
} else {
host_data_clear_flag(VCPU_IN_HYP_CONTEXT);
+
+ if (guest_hcr & HCR_NV) {
+ u64 va = __fix_to_virt(vncr_fixmap(smp_processor_id()));
+
+ /* Inherit the low bits from the actual register */
+ va |= __vcpu_sys_reg(vcpu, VNCR_EL2) & GENMASK(PAGE_SHIFT - 1, 0);
+ write_sysreg_s(va, SYS_VNCR_EL2);
+
+ /* Force NV2 in case the guest is forgetful... */
+ guest_hcr |= HCR_NV2;
+ }
}

- return hcr | (__vcpu_sys_reg(vcpu, HCR_EL2) & ~NV_HCR_GUEST_EXCLUDE);
+ BUG_ON(host_data_test_flag(VCPU_IN_HYP_CONTEXT) &&
+ host_data_test_flag(L1_VNCR_MAPPED));
+
+ return hcr | (guest_hcr & ~NV_HCR_GUEST_EXCLUDE);
}

static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
--
2.39.2