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

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Message-ID: <79eaa1d4671c7bc93910ca3399bf5b023c52efa6.camel@intel.com>
Date: Mon, 19 May 2025 22:34:14 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Reshetova, Elena" <elena.reshetova@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "linux-sgx@...r.kernel.org"
	<linux-sgx@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, "Scarlata,
 Vincent R" <vincent.r.scarlata@...el.com>, "Raynor, Scott"
	<scott.raynor@...el.com>, "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>,
	"jarkko@...nel.org" <jarkko@...nel.org>, "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 11:47 +0000, Reshetova, Elena wrote:
> > 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.
> 
> 
> Could you please elaborate a bit more on this? 
> In case sgx_inc_usage_count fails, we dont allocate resources yet, so what is 
> wrong? 
> 

I haven't looked into (details of) the last patch yet, but for _this_ patch
only, doing sgx_inc_usage_count() at the beginning of sgx_open() will result in
the usage count being increased even when sgx_open() fails at a later time. 
Since sgx_release() is not called when sgx_open() fails, the usage count will
not be decreased correctly.

No?