> -----Original Message-----
> From: Hansen, Dave <dave.han...@intel.com>
> Sent: Friday, August 1, 2025 8:13 PM
> To: Reshetova, Elena <elena.reshet...@intel.com>
> Cc: jar...@kernel.org; sea...@google.com; Huang, Kai
> <kai.hu...@intel.com>; mi...@kernel.org; linux-...@vger.kernel.org; linux-
> ker...@vger.kernel.org; x...@kernel.org; Mallick, Asit K
> <asit.k.mall...@intel.com>; Scarlata, Vincent R
> <vincent.r.scarl...@intel.com>;
> Cai, Chong <cho...@google.com>; Aktas, Erdem <erdemak...@google.com>;
> Annapurve, Vishal <vannapu...@google.com>; Bondarevska, Nataliia
> <bond...@google.com>; Raynor, Scott <scott.ray...@intel.com>
> Subject: Re: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]
>
> The changelog is missing a tidbit about the fact that this is still dead
> code until sgx_inc_usage_count() gets a real implementation.
Will add.
>
> On 8/1/25 04:25, Elena Reshetova wrote:
> ...
> > +/**
> > + * sgx_update_svn() - Attempt to call ENCLS[EUPDATESVN].
> > + * This instruction attempts to update CPUSVN to the
> > + * currently loaded microcode update SVN and generate new
> > + * cryptographic assets. Must be called when EPC is empty.
>
> As a general rule, I'd much rather have the "Must be $FOO" rules written
> in code than in a comment, or along with a comment:
>
> /* EPC is guaranteed to be empty when there are no users: */
> WARN(count, "Elevated usage count...");
I will change to do it this way.
>
> > + * Most of the time, there will be no update and that's OK.
>
> This should go with the check for SGX_NO_UPDATE, not here.
Ok, will fix.
>
> > + * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
> > + * operation can be safely retried. In other failure cases,
> > + * the retry should not be attempted.
>
> Ditto. This is rewriting the code in comments.
Ok, will drop.
>
> > + * Return:
> > + * 0: Success or not supported
> > + * -EAGAIN: Can be safely retried, failure is due to lack of
> > + * entropy in RNG.
> > + * -EIO: Unexpected error, retries are not advisable.
> > + */
> > +static int __maybe_unused sgx_update_svn(void)
> > +{
> > + int ret;
> > +
> > + /*
> > + * If EUPDATESVN is not available, it is ok to
> > + * silently skip it to comply with legacy behavior.
> > + */
> > + if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
> > + return 0;
> > +
> > + for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
> > + ret = __eupdatesvn();
> > +
> > + /* Stop on success or unexpected errors: */
> > + if (ret != SGX_INSUFFICIENT_ENTROPY)
> > + break;
> > + }
> > +
> > + /*
> > + * SVN successfully updated.
> > + * Let users know when the update was successful.
> > + */
> > + if (!ret)
> > + pr_info("SVN updated successfully\n");
> > +
> > + if (!ret || ret == SGX_NO_UPDATE)
> > + return 0;
> > +
> > + /*
> > + * SVN update failed due to lack of entropy in DRNG.
> > + * Indicate to userspace that it should retry.
> > + */
> > + if (ret == SGX_INSUFFICIENT_ENTROPY)
> > + return -EAGAIN;
>
> There are four cases to handle. Doesn't it make sense to just write it
> as four literal "case"s?
>
> switch (ret) {
> case 0:
> pr_info("...");
> return 0;
> case SGX_NO_UPDATE:
> return 0;
> case SGX_INSUFFICIENT_ENTROPY:
> return -EAGAIN;
> default:
> break;
> }
>
>
Will re-write accordingly.
Thank you very much for your prompt review Dave!
Best Regards,
Elena.
