> -----Original Message----- > From: Huang, Kai <[email protected]> > Sent: Monday, August 11, 2025 11:37 PM > To: Reshetova, Elena <[email protected]>; Hansen, Dave > <[email protected]> > Cc: [email protected]; [email protected]; Scarlata, Vincent R > <[email protected]>; [email protected]; [email protected]; > Annapurve, Vishal <[email protected]>; [email protected]; > Mallick, Asit K <[email protected]>; Aktas, Erdem > <[email protected]>; Cai, Chong <[email protected]>; Bondarevska, > Nataliia <[email protected]>; [email protected]; Raynor, Scott > <[email protected]> > 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.
