linux-kernel - Re: [PATCH v5 1/5] x86/sgx: Introduce a counter to count the sgx_(vepc

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Message-ID: <c955515c5469dae17faa13ebda28459d7c998bb9.camel@intel.com>
Date: Mon, 19 May 2025 10:47:29 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Reshetova, Elena" <elena.reshetova@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>
CC: "Raynor, Scott" <scott.raynor@...el.com>, "linux-sgx@...r.kernel.org"
	<linux-sgx@...r.kernel.org>, "Scarlata, Vincent R"
	<vincent.r.scarlata@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"jarkko@...nel.org" <jarkko@...nel.org>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>, "Cai, Chong" <chongc@...gle.com>,
	"bondarn@...gle.com" <bondarn@...gle.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "dionnaglaze@...gle.com" <dionnaglaze@...gle.com>
Subject: Re: [PATCH v5 1/5] x86/sgx: Introduce a counter to count the
 sgx_(vepc_)open()

On Mon, 2025-05-19 at 10:24 +0300, Elena Reshetova wrote:
> 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.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> ---
>  arch/x86/kernel/cpu/sgx/driver.c |  1 +
>  arch/x86/kernel/cpu/sgx/encl.c   |  1 +
>  arch/x86/kernel/cpu/sgx/main.c   | 14 ++++++++++++++
>  arch/x86/kernel/cpu/sgx/sgx.h    |  3 +++
>  arch/x86/kernel/cpu/sgx/virt.c   |  2 ++
>  5 files changed, 21 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
> index 7f8d1e11dbee..b5ffe104af4c 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -19,6 +19,7 @@ static int sgx_open(struct inode *inode, struct file *file)
>  	struct sgx_encl *encl;
>  	int ret;
>  
> +	sgx_inc_usage_count();

This should be done at the end of sgx_open() where the open cannot fail, since
sgx_release() is not called if sgx_open() failed AFAICT.

>  	encl = kzalloc(sizeof(*encl), GFP_KERNEL);
>  	if (!encl)
>  		return -ENOMEM;
> 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 8ce352fc72ac..80d565e6f2ad 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -914,6 +914,20 @@ int sgx_set_attribute(unsigned long *allowed_attributes,
>  }
>  EXPORT_SYMBOL_GPL(sgx_set_attribute);
>  
> +/* Counter to count the active SGX users */
> +static atomic64_t sgx_usage_count;
> +
> +int sgx_inc_usage_count(void)
> +{
> +	atomic64_inc(&sgx_usage_count);
> +	return 0;
> +}

What's the purpose of the returning int?  Seems no caller uses the return value.

> +
> +void sgx_dec_usage_count(void)
> +{
> +	atomic64_dec(&sgx_usage_count);
> +}
> +
>  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 7aaa3652e31d..83de0907f32c 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;
>  }
>  
> @@ -262,6 +263,7 @@ static int sgx_vepc_open(struct inode *inode, struct file *file)
>  {
>  	struct sgx_vepc *vepc;
>  
> +	sgx_inc_usage_count();

Ditto to sgx_open().

>  	vepc = kzalloc(sizeof(struct sgx_vepc), GFP_KERNEL);
>  	if (!vepc)
>  		return -ENOMEM;