linux-kernel - [PATCH v9 2/6] x86/sgx: Introduce a counter to count the sgx_(vepc

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Message-ID: <20250724080313.605676-3-elena.reshetova@intel.com>
Date: Thu, 24 Jul 2025 11:02:11 +0300
From: Elena Reshetova <elena.reshetova@...el.com>
To: dave.hansen@...el.com
Cc: jarkko@...nel.org,
	seanjc@...gle.com,
	kai.huang@...el.com,
	mingo@...nel.org,
	linux-sgx@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	asit.k.mallick@...el.com,
	vincent.r.scarlata@...el.com,
	chongc@...gle.com,
	erdemaktas@...gle.com,
	vannapurve@...gle.com,
	bondarn@...gle.com,
	scott.raynor@...el.com,
	Elena Reshetova <elena.reshetova@...el.com>
Subject: [PATCH v9 2/6] x86/sgx: Introduce a counter to count the sgx_(vepc_)open()

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@...gle.com>
Signed-off-by: Elena Reshetova <elena.reshetova@...el.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