Re: [PATCH v4 16/26] KVM: kvm_arch.c: Remove a global variable, hardware_enable_failed

[Chao Gao]

On Thu, Sep 08, 2022 at 04:25:32PM -0700, isaku.yamahata@xxxxxxxxx wrote:
>From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>
>A global variable hardware_enable_failed in kvm_arch.c is used only by
>kvm_arch_add_vm() and hardware_enable().  It doesn't have to be a global
>variable.  Make it function local.
>
>Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>

>---
> virt/kvm/kvm_arch.c | 62 ++++++++++++++++++++++-----------------------
> 1 file changed, 31 insertions(+), 31 deletions(-)
>
>diff --git a/virt/kvm/kvm_arch.c b/virt/kvm/kvm_arch.c
>index 4fe16e8ef2e5..ad23537ebe3b 100644
>--- a/virt/kvm/kvm_arch.c
>+++ b/virt/kvm/kvm_arch.c
>@@ -13,14 +13,13 @@
> #include <linux/kvm_host.h>
> 
> static cpumask_t cpus_hardware_enabled = CPU_MASK_NONE;
>-static atomic_t hardware_enable_failed;
> 
> __weak int kvm_arch_post_init_vm(struct kvm *kvm)
> {
> 	return 0;
> }
> 
>-static void hardware_enable(void *caller_name)
>+static int __hardware_enable(void *caller_name)

nit: caller_name can be dropped and use __builtin_return_address(0) instead.

> {
> 	int cpu = raw_smp_processor_id();
> 	int r;
>@@ -28,18 +27,22 @@ static void hardware_enable(void *caller_name)
> 	WARN_ON_ONCE(preemptible());
> 
> 	if (cpumask_test_cpu(cpu, &cpus_hardware_enabled))
>-		return;
>-
>-	cpumask_set_cpu(cpu, &cpus_hardware_enabled);
>-
>+		return 0;
> 	r = kvm_arch_hardware_enable();
>-
>-	if (r) {
>-		cpumask_clear_cpu(cpu, &cpus_hardware_enabled);
>-		atomic_inc(&hardware_enable_failed);
>+	if (r)
> 		pr_warn("kvm: enabling virtualization on CPU%d failed during %s()\n",
> 			cpu, (const char *)caller_name);
>-	}
>+	else
>+		cpumask_set_cpu(cpu, &cpus_hardware_enabled);
>+	return r;
>+}
>+
>+static void hardware_enable(void *arg)
>+{
>+	atomic_t *failed = arg;
>+
>+	if (__hardware_enable((void *)__func__))
>+		atomic_inc(failed);
> }
> 
> static void hardware_disable(void *junk)
>@@ -65,15 +68,16 @@ __weak void kvm_arch_pre_hardware_unsetup(void)
>  */
> __weak int kvm_arch_add_vm(struct kvm *kvm, int usage_count)
> {
>+	atomic_t failed;

nit:
	atomic_t failed = ATOMIC_INIT(0);

then you can drop the atomic_set() below.

> 	int r = 0;
> 
> 	if (usage_count != 1)
> 		return 0;
> 
>-	atomic_set(&hardware_enable_failed, 0);
>-	on_each_cpu(hardware_enable, (void *)__func__, 1);
>+	atomic_set(&failed, 0);
>+	on_each_cpu(hardware_enable, &failed, 1);
> 
>-	if (atomic_read(&hardware_enable_failed)) {
>+	if (atomic_read(&failed)) {
> 		r = -EBUSY;
> 		goto err;
> 	}
>@@ -96,33 +100,29 @@ __weak int kvm_arch_del_vm(int usage_count)
> 
> __weak int kvm_arch_online_cpu(unsigned int cpu, int usage_count)
> {
>-	int ret = 0;
>+	int ret;
> 
> 	ret = kvm_arch_check_processor_compat();
> 	if (ret)
> 		return ret;
> 
>+	if (!usage_count)
>+		return 0;
>+
>+	/*
>+	 * arch callback kvm_arch_hardware_eanble() assumes that

						^ enable