On 02/02/2025 06:41, Gavin Shan wrote:

On 12/13/24 1:55 AM, Steven Price wrote:

quoted

From: Joey Gouly <joey.gouly@arm.com>

Forward RSI_HOST_CALLS to KVM's HVC handler.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
Changes since v4:
  * Setting GPRS is now done by kvm_rec_enter() rather than
    rec_exit_host_call() (see previous patch - arm64: RME: Handle realm
    enter/exit). This fixes a bug where the registers set by user space
    were being ignored.
---
  arch/arm64/kvm/rme-exit.c | 22 ++++++++++++++++++++++
  1 file changed, 22 insertions(+)

diff --git a/arch/arm64/kvm/rme-exit.c b/arch/arm64/kvm/rme-exit.c
index 8f0f9ab57f28..b2a367474d74 100644
--- a/arch/arm64/kvm/rme-exit.c
+++ b/arch/arm64/kvm/rme-exit.c

@@ -103,6 +103,26 @@ static int rec_exit_ripas_change(struct kvm_vcpu

*vcpu)
      return 0;
  }
  +static int rec_exit_host_call(struct kvm_vcpu *vcpu)
+{
+    int ret, i;
+    struct realm_rec *rec = &vcpu->arch.rec;
+
+    vcpu->stat.hvc_exit_stat++;
+
+    for (i = 0; i < REC_RUN_GPRS; i++)
+        vcpu_set_reg(vcpu, i, rec->run->exit.gprs[i]);
+
+    ret = kvm_smccc_call_handler(vcpu);
+
+    if (ret < 0) {
+        vcpu_set_reg(vcpu, 0, ~0UL);
+        ret = 1;
+    }
+
+    return ret;
+}
+

It seems that the return value from kvm_smccc_call() won't be negative.

Well the comment above kvm_psci_call() explains that the return value
can be negative which would be passed through, so there's definitely a
convention that it could be negative. However...

Besides,
the host call requests are currently handled by kvm_psci_call(), which
isn't
what we want.

Indeed, we shouldn't be getting PSCI calls this way as the RMM needs to
be involved for proper handling of PSCI.

So I think a new helper is needed and called in> kvm_smccc_call_handler().
The new helper simply push the error (NOT_SUPPORTED) to x0. Otherwise, a
unexpected
return value will be seen by guest.

handle_rec_exit
  rec_exit_host_call
    kvm_smccc_call_handler

I'm not sure I follow here. Are you saying that we should have separate
handling of HOST_CALLs to SMCCC? That's certainly a possibility, but the
expectation is that HOST_CALL is effectively equivalent to a simple
SMC/HVC call in a normal guest. To be honest a "Realm Host Interface" is
something that we're currently lacking a spec for.

Thanks,
Steve

quoted

  static void update_arch_timer_irq_lines(struct kvm_vcpu *vcpu)
  {
      struct realm_rec *rec = &vcpu->arch.rec;

@@ -164,6 +184,8 @@ int handle_rec_exit(struct kvm_vcpu *vcpu, int

rec_run_ret)
          return rec_exit_psci(vcpu);
      case RMI_EXIT_RIPAS_CHANGE:
          return rec_exit_ripas_change(vcpu);
+    case RMI_EXIT_HOST_CALL:
+        return rec_exit_host_call(vcpu);
      }
        kvm_pr_unimpl("Unsupported exit reason: %u\n",

Thanks,
Gavin