Re: [PATCH] KVM: arm64: Fix the return value of smp_call_function_single()

From: Marc Zyngier
Date: Mon Jan 18 2021 - 06:22:41 EST

On 2021-01-18 09:31, Yejune Deng wrote:
In smp_call_function_single(), the 3rd parameter isn't the return value
and it's always positive. But it may return a negative value. So the
'ret' is should be the return value of the smp_call_function_single().

In check_kvm_target_cpu(), 'phys_target' is more readable than 'ret'.

Signed-off-by: Yejune Deng <yejune.deng@xxxxxxxxx>
arch/arm64/kvm/arm.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 04c44853b103..5fa5c04106de 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1815,9 +1815,9 @@ static int init_hyp_mode(void)
return err;

-static void check_kvm_target_cpu(void *ret)
+static void check_kvm_target_cpu(void *phys_target)
- *(int *)ret = kvm_target_cpu();
+ *(int *)phys_target = kvm_target_cpu();

struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr)
@@ -1879,7 +1879,7 @@ void kvm_arch_irq_bypass_start(struct
irq_bypass_consumer *cons)
int kvm_arch_init(void *opaque)
int err;
- int ret, cpu;
+ int ret, cpu, phys_target;
bool in_hyp_mode;

if (!is_hyp_mode_available()) {
@@ -1900,7 +1900,7 @@ int kvm_arch_init(void *opaque)
"Only trusted guests should be used on this system.\n");

for_each_online_cpu(cpu) {
- smp_call_function_single(cpu, check_kvm_target_cpu, &ret, 1);
+ ret = smp_call_function_single(cpu, check_kvm_target_cpu, &phys_target, 1);
if (ret < 0) {
kvm_err("Error, CPU %d not supported!\n", cpu);
return -ENODEV;

That's not the purpose of this code. We check the target CPU
for so that we can decide to *fail* the KVM init if there is
a CPU we do not support (we definitely used to do that with
32bit), and the error message clearly states this.

So if you want to handle a cross-call failure, please do that.
But don't change the existing semantics of this code.

Jazz is not dead. It just smells funny...