From: Isaku Yamahata <isaku.yamahata@intel.com>

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@intel.com>
---
 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)
 {
 	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;
 	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
+	 * preemption is disabled for historical reason.  Disable
+	 * preemption until all arch callbacks are fixed.
+	 */
+	preempt_disable();
 	/*
 	 * Abort the CPU online process if hardware virtualization cannot
 	 * be enabled. Otherwise running VMs would encounter unrecoverable
 	 * errors when scheduled to this CPU.
 	 */
-	if (usage_count) {
-		WARN_ON_ONCE(atomic_read(&hardware_enable_failed));
+	ret = __hardware_enable((void *)__func__);
+	preempt_enable();
 
-		/*
-		 * arch callback kvm_arch_hardware_eanble() assumes that
-		 * preemption is disabled for historical reason.  Disable
-		 * preemption until all arch callbacks are fixed.
-		 */
-		preempt_disable();
-		hardware_enable((void *)__func__);
-		preempt_enable();
-		if (atomic_read(&hardware_enable_failed)) {
-			atomic_set(&hardware_enable_failed, 0);
-			ret = -EIO;
-		}
-	}
 	return ret;
 }
 
@@ -168,7 +168,7 @@ __weak void kvm_arch_resume(int usage_count)
 
 	if (usage_count) {
 		preempt_disable();
-		hardware_enable((void *)__func__);
+		(void)__hardware_enable((void *)__func__);
 		preempt_enable();
 	}
 }
-- 
2.25.1

On Thu, Sep 08, 2022 at 04:25:32PM -0700, isaku.yamahata@intel.com wrote:
>From: Isaku Yamahata <isaku.yamahata@intel.com>
>
>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@intel.com>

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

>---
> 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

On Fri, Sep 09, 2022 at 02:54:05PM +0800,
Chao Gao <chao.gao@intel.com> wrote:

> >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.

Do you want to update your patch
"KVM: Provide more information in kernel log if hardware enabling fails"?
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>