> -----Original Message----- > From: Huang, Kai <[email protected]> > Sent: Friday, August 15, 2025 12:41 AM > 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 v14 5/5] x86/sgx: Enable automatic SVN updates for SGX > enclaves > > On Thu, 2025-08-14 at 09:50 -0700, Dave Hansen wrote: > > On 8/14/25 00:34, Elena Reshetova wrote: > > > +/* Mutex to ensure no concurrent EPC accesses during EUPDATESVN */ > > > +static DEFINE_MUTEX(sgx_svn_lock); > > > + > > > int sgx_inc_usage_count(void) > > > { > > > + int ret; > > > + > > > + guard(mutex)(&sgx_svn_lock); > > > + > > > + if (!sgx_usage_count) { > > > + ret = sgx_update_svn(); > > > + if (ret) > > > + return ret; > > > + } > > > + > > > + sgx_usage_count++; > > > + > > > return 0; > > > } > > > > > > void sgx_dec_usage_count(void) > > > { > > > - return; > > > + sgx_usage_count--; > > > } > > > > How is a plain int-- safe? > > > > Where's the locking? > > Sorry I missed this during review too.
My line of thinking went that we don't actually care or act on decrement (it is not a true ref counter) and therefore, races here are ok. What I forgot is that we loose basic atomicity also with plain int (( I would personally like to go back to atomic (this is what it is exactly for), but I can also just add another mutex here. Preferences? Best Regards, Elena.
