> -----Original Message-----
> From: Huang, Kai <kai.hu...@intel.com>
> Sent: Monday, August 11, 2025 11:37 PM
> To: Reshetova, Elena <elena.reshet...@intel.com>; Hansen, Dave
> <dave.han...@intel.com>
> Cc: linux-...@vger.kernel.org; mi...@kernel.org; Scarlata, Vincent R
> <vincent.r.scarl...@intel.com>; x...@kernel.org; jar...@kernel.org;
> Annapurve, Vishal <vannapu...@google.com>; linux-kernel@vger.kernel.org;
> Mallick, Asit K <asit.k.mall...@intel.com>; Aktas, Erdem
> <erdemak...@google.com>; Cai, Chong <cho...@google.com>; Bondarevska,
> Nataliia <bond...@google.com>; sea...@google.com; Raynor, Scott
> <scott.ray...@intel.com>
> Subject: Re: [PATCH v12 5/5] x86/sgx: Enable automatic SVN updates for SGX
> enclaves
>
> > >
> > > >
> > > > +/* Mutex to ensure no concurrent EPC accesses during EUPDATESVN */
> > > > +static DEFINE_MUTEX(sgx_svn_lock);
> > > > +
> > > > int sgx_inc_usage_count(void)
> > > > {
> > > > + guard(mutex)(&sgx_svn_lock);
> > > > +
> > > > + if (sgx_usage_count++ == 0)
> > > > + return sgx_update_svn();
> > > > +
> > >
> > > Hmm.. sorry for not noticing this before.. But I think we might have a
> > > problem here since the sgx_usage_count is increased regardless of the
> > > result of sgx_update_svn().
> > >
> > > If sgx_update_svn() fails, it makes sgx_inc_usage_count() return error
> > > too, so sgx_{vepc_}open() will fail and return immediately w/o calling
> > > sgx_dec_usage_count().
> > >
> > > But the sgx_usage_count has been increased.
> > >
> > > AFAICT when sgx_{vepc_}_open() fails, the sgx_{vepc_}release() is not
> > > called, so sgx_dec_usage_count() is never called and sgx_usage_count
> > > remains increased.
> > >
> > > So when sgx_{vepc_}open() calls sgx_inc_usage_count() again, it will skip
> > > calling sgx_update_svn(), and allow enclave/vEPC to be created
> > > successfully, which just defeats the purpose.
> > >
> > > So if I am not missing anything, I think we should only increase the count
> > > when sgx_update_svn() returns success?
> >
> > Yes, you are right, thanks for catching this! In past the atomic version of
> > this patch did exactly, but after I went into this simplified version of
> > counting,
> > this angle got broken.
> > Will fix.
>
> Btw, I noticed this when I was looking at:
>
> WARN(sgx_usage_count != 1, "...");
>
> in patch 4 and wondering why it's not "!= 0".
>
> Please don't forget to update that when needed.
Yes, of course.
