Currently SGX does not have a global counter to count the
active users from userspace or hypervisor. Implement such a counter,
sgx_usage_count. It will be used by the driver when attempting
to call EUPDATESVN SGX instruction.

Note: the sgx_inc_usage_count prototype is defined to return
int for the cleanliness of the follow-up patches. When the
EUPDATESVN SGX instruction will be enabled in the follow-up patch,
the sgx_inc_usage_count will start to return int.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/kernel/cpu/sgx/driver.c | 19 ++++++++++++++++++-
 arch/x86/kernel/cpu/sgx/encl.c   |  1 +
 arch/x86/kernel/cpu/sgx/main.c   | 13 +++++++++++++
 arch/x86/kernel/cpu/sgx/sgx.h    |  3 +++
 arch/x86/kernel/cpu/sgx/virt.c   | 21 ++++++++++++++++++++-
 5 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index 9aa48f455c54..79d6020dfe9c 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -41,6 +41,23 @@ static int __sgx_open(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static int sgx_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = sgx_inc_usage_count();
+	if (ret)
+		return ret;
+
+	ret = __sgx_open(inode, file);
+	if (ret) {
+		sgx_dec_usage_count();
+		return ret;
+	}
+
+	return 0;
+}
+
 static int sgx_release(struct inode *inode, struct file *file)
 {
 	struct sgx_encl *encl = file->private_data;
@@ -126,7 +143,7 @@ static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,
 
 static const struct file_operations sgx_encl_fops = {
 	.owner			= THIS_MODULE,
-	.open			= __sgx_open,
+	.open			= sgx_open,
 	.release		= sgx_release,
 	.unlocked_ioctl		= sgx_ioctl,
 #ifdef CONFIG_COMPAT
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 279148e72459..3b54889ae4a4 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -765,6 +765,7 @@ void sgx_encl_release(struct kref *ref)
 	WARN_ON_ONCE(encl->secs.epc_page);
 
 	kfree(encl);
+	sgx_dec_usage_count();
 }
 
 /*
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 2de01b379aa3..ccb81a649d1b 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -917,6 +917,19 @@ int sgx_set_attribute(unsigned long *allowed_attributes,
 }
 EXPORT_SYMBOL_GPL(sgx_set_attribute);
 
+/* Counter to count the active SGX users */
+static int __maybe_unused sgx_usage_count;
+
+int sgx_inc_usage_count(void)
+{
+	return 0;
+}
+
+void sgx_dec_usage_count(void)
+{
+	return;
+}
+
 static int __init sgx_init(void)
 {
 	int ret;
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index d2dad21259a8..f5940393d9bd 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -102,6 +102,9 @@ static inline int __init sgx_vepc_init(void)
 }
 #endif
 
+int sgx_inc_usage_count(void);
+void sgx_dec_usage_count(void);
+
 void sgx_update_lepubkeyhash(u64 *lepubkeyhash);
 
 #endif /* _X86_SGX_H */
diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
index d8fdf7f39215..d6bff258d761 100644
--- a/arch/x86/kernel/cpu/sgx/virt.c
+++ b/arch/x86/kernel/cpu/sgx/virt.c
@@ -255,6 +255,7 @@ static int sgx_vepc_release(struct inode *inode, struct file *file)
 	xa_destroy(&vepc->page_array);
 	kfree(vepc);
 
+	sgx_dec_usage_count();
 	return 0;
 }
 
@@ -265,6 +266,7 @@ static int __sgx_vepc_open(struct inode *inode, struct file *file)
 	vepc = kzalloc(sizeof(struct sgx_vepc), GFP_KERNEL);
 	if (!vepc)
 		return -ENOMEM;
+
 	mutex_init(&vepc->lock);
 	xa_init(&vepc->page_array);
 
@@ -273,6 +275,23 @@ static int __sgx_vepc_open(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static int sgx_vepc_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = sgx_inc_usage_count();
+	if (ret)
+		return ret;
+
+	ret =  __sgx_vepc_open(inode, file);
+	if (ret) {
+		sgx_dec_usage_count();
+		return ret;
+	}
+
+	return 0;
+}
+
 static long sgx_vepc_ioctl(struct file *file,
 			   unsigned int cmd, unsigned long arg)
 {
@@ -291,7 +310,7 @@ static long sgx_vepc_ioctl(struct file *file,
 
 static const struct file_operations sgx_vepc_fops = {
 	.owner		= THIS_MODULE,
-	.open		= __sgx_vepc_open,
+	.open		= sgx_vepc_open,
 	.unlocked_ioctl	= sgx_vepc_ioctl,
 	.compat_ioctl	= sgx_vepc_ioctl,
 	.release	= sgx_vepc_release,
-- 
2.45.2

>  
> +static int sgx_open(struct inode *inode, struct file *file)
> +{
> +	int ret;
> +
> +	ret = sgx_inc_usage_count();
> +	if (ret)
> +		return ret;
> +
> +	ret = __sgx_open(inode, file);
> +	if (ret) {
> +		sgx_dec_usage_count();
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  static int sgx_release(struct inode *inode, struct file *file)
>  {
>  	struct sgx_encl *encl = file->private_data;
> @@ -126,7 +143,7 @@ static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,
>  
>  static const struct file_operations sgx_encl_fops = {
>  	.owner			= THIS_MODULE,
> -	.open			= __sgx_open,
> +	.open			= sgx_open,

If you merge the first patch to this one, you can avoid such chunk in the
diff.

In fact, I think merging the first patch to this one makes sense because
__sgx_open() only makes sense when you have sgx_inc_usage_count().

[...]

>  
> +/* Counter to count the active SGX users */
> +static int __maybe_unused sgx_usage_count;

As replied to the patch 6, I think you can just introduce this variable in
that patch.

> +
> +int sgx_inc_usage_count(void)
> +{
> +	return 0;
> +}
> +
> +void sgx_dec_usage_count(void)
> +{
> +	return;
> +}
> +
> 

[...]

> @@ -265,6 +266,7 @@ static int __sgx_vepc_open(struct inode *inode, struct file *file)
>  	vepc = kzalloc(sizeof(struct sgx_vepc), GFP_KERNEL);
>  	if (!vepc)
>  		return -ENOMEM;
> +

Unintended change?

>  	mutex_init(&vepc->lock);
>  	xa_init(&vepc->page_array);
>  
> @@ -273,6 +275,23 @@ static int __sgx_vepc_open(struct inode *inode, struct file *file)
>  	return 0;
>  }
>  
> +static int sgx_vepc_open(struct inode *inode, struct file *file)
> +{
> +	int ret;
> +
> +	ret = sgx_inc_usage_count();
> +	if (ret)
> +		return ret;
> +
> +	ret =  __sgx_vepc_open(inode, file);
> +	if (ret) {
> +		sgx_dec_usage_count();
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  static long sgx_vepc_ioctl(struct file *file,
>  			   unsigned int cmd, unsigned long arg)
>  {
> @@ -291,7 +310,7 @@ static long sgx_vepc_ioctl(struct file *file,
>  
>  static const struct file_operations sgx_vepc_fops = {
>  	.owner		= THIS_MODULE,
> -	.open		= __sgx_vepc_open,
> +	.open		= sgx_vepc_open,

Ditto to sgx_open().

> -----Original Message-----
> From: Huang, Kai <kai.huang@intel.com>
> Sent: Thursday, July 24, 2025 1:25 PM
> To: Reshetova, Elena <elena.reshetova@intel.com>; Hansen, Dave
> <dave.hansen@intel.com>
> Cc: seanjc@google.com; mingo@kernel.org; Scarlata, Vincent R
> <vincent.r.scarlata@intel.com>; x86@kernel.org; jarkko@kernel.org;
> Annapurve, Vishal <vannapurve@google.com>; linux-kernel@vger.kernel.org;
> Mallick, Asit K <asit.k.mallick@intel.com>; Aktas, Erdem
> <erdemaktas@google.com>; Cai, Chong <chongc@google.com>; Bondarevska,
> Nataliia <bondarn@google.com>; linux-sgx@vger.kernel.org; Raynor, Scott
> <scott.raynor@intel.com>
> Subject: Re: [PATCH v9 2/6] x86/sgx: Introduce a counter to count the
> sgx_(vepc_)open()

Thank you very much for your review Kai!

> 
> 
> >
> > +static int sgx_open(struct inode *inode, struct file *file)
> > +{
> > +	int ret;
> > +
> > +	ret = sgx_inc_usage_count();
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = __sgx_open(inode, file);
> > +	if (ret) {
> > +		sgx_dec_usage_count();
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int sgx_release(struct inode *inode, struct file *file)
> >  {
> >  	struct sgx_encl *encl = file->private_data;
> > @@ -126,7 +143,7 @@ static long sgx_compat_ioctl(struct file *filep,
> unsigned int cmd,
> >
> >  static const struct file_operations sgx_encl_fops = {
> >  	.owner			= THIS_MODULE,
> > -	.open			= __sgx_open,
> > +	.open			= sgx_open,
> 
> If you merge the first patch to this one, you can avoid such chunk in the
> diff.

Yes, agree, I would have likely squashed whole this series into one patch,
but in this case I followed Jarkko's suggestion to do renaming of the
functions in the separate patch. 

> 
> In fact, I think merging the first patch to this one makes sense because
> __sgx_open() only makes sense when you have sgx_inc_usage_count().

Yes, agree, but again this would be against the suggestion I got previously.

> 
> [...]
> 
> >
> > +/* Counter to count the active SGX users */
> > +static int __maybe_unused sgx_usage_count;
> 
> As replied to the patch 6, I think you can just introduce this variable in
> that patch.

Yes, now that I dropped the sgx_usage_count fully
I guess it can be also defined in patch 6, albeit it was a bit
more logical imo to have it defined as unused already here
since we are introducing counting primitives. 

> 
> > +
> > +int sgx_inc_usage_count(void)
> > +{
> > +	return 0;
> > +}
> > +
> > +void sgx_dec_usage_count(void)
> > +{
> > +	return;
> > +}
> > +
> >
> 
> [...]
> 
> > @@ -265,6 +266,7 @@ static int __sgx_vepc_open(struct inode *inode,
> struct file *file)
> >  	vepc = kzalloc(sizeof(struct sgx_vepc), GFP_KERNEL);
> >  	if (!vepc)
> >  		return -ENOMEM;
> > +
> 
> Unintended change?

Ups, yes, missed this one, will fix.

> 
> >  	mutex_init(&vepc->lock);
> >  	xa_init(&vepc->page_array);
> >
> > @@ -273,6 +275,23 @@ static int __sgx_vepc_open(struct inode *inode,
> struct file *file)
> >  	return 0;
> >  }
> >
> > +static int sgx_vepc_open(struct inode *inode, struct file *file)
> > +{
> > +	int ret;
> > +
> > +	ret = sgx_inc_usage_count();
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret =  __sgx_vepc_open(inode, file);
> > +	if (ret) {
> > +		sgx_dec_usage_count();
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static long sgx_vepc_ioctl(struct file *file,
> >  			   unsigned int cmd, unsigned long arg)
> >  {
> > @@ -291,7 +310,7 @@ static long sgx_vepc_ioctl(struct file *file,
> >
> >  static const struct file_operations sgx_vepc_fops = {
> >  	.owner		= THIS_MODULE,
> > -	.open		= __sgx_vepc_open,
> > +	.open		= sgx_vepc_open,
> 
> Ditto to sgx_open().

Yes, if patches are merged, this would go away.
Jarkko, are ok with merging or do you still believe it
it better to have it as separate patches? 

Best Regards,
Elena.