[PATCH v6 21/64] KVM: arm64: nv: Handle PSCI call via smc from the guest

Marc Zyngier
2022-01-28T12:31:59Z

From: Jintack Lim <jintack.lim@linaro.org>

VMs used to execute hvc #0 for the psci call if EL3 is not implemented.
However, when we come to provide the virtual EL2 mode to the VM, the
host OS inside the VM calls kvm_call_hyp() which is also hvc #0. So,
it's hard to differentiate between them from the host hypervisor's point
of view.

So, let the VM execute smc instruction for the psci call. On ARMv8.3,
even if EL3 is not implemented, a smc instruction executed at non-secure
EL1 is trapped to EL2 if HCR_EL2.TSC==1, rather than being treated as
UNDEFINED. So, the host hypervisor can handle this psci call without any
confusion.

Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/handle_exit.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 2bbeed8c9786..0cedef6e0d80 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -62,6 +62,8 @@ static int handle_hvc(struct kvm_vcpu *vcpu)

static int handle_smc(struct kvm_vcpu *vcpu)
{
+ int ret;
+
/*
* "If an SMC instruction executed at Non-secure EL1 is
* trapped to EL2 because HCR_EL2.TSC is 1, the exception is a
@@ -69,10 +71,28 @@ static int handle_smc(struct kvm_vcpu *vcpu)
*
* We need to advance the PC after the trap, as it would
* otherwise return to the same address...
+ *
+ * If imm is non-zero, it's not defined, so just skip it.
+ */
+ if (kvm_vcpu_hvc_get_imm(vcpu)) {
+ vcpu_set_reg(vcpu, 0, ~0UL);
+ kvm_incr_pc(vcpu);
+ return 1;
+ }
+
+ /*
+ * If imm is zero, it's a psci call.
+ * Note that on ARMv8.3, even if EL3 is not implemented, SMC executed
+ * at Non-secure EL1 is trapped to EL2 if HCR_EL2.TSC==1, rather than
+ * being treated as UNDEFINED.
*/
- vcpu_set_reg(vcpu, 0, ~0UL);
+ ret = kvm_hvc_call_handler(vcpu);
+ if (ret < 0)
+ vcpu_set_reg(vcpu, 0, ~0UL);
+
kvm_incr_pc(vcpu);
- return 1;
+
+ return ret;
}

/*