> >
> > +/**
> > + * sgx_updatesvn() - Attempt to call ENCLS[EUPDATESVN].
>
> sgx_updatesvn() -> sgx_update_svn():
>
> arch/x86/kernel/cpu/sgx/main.c:941: warning: expecting prototype for
> sgx_updatesvn(). Prototype was for sgx_update_svn() instead
>
>
> > + * 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.
> > + * Most of the time, there will be no update and that's OK.
> > + * 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.
> > + *
> > + * 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 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 was already up-to-date. This is the most
> > + * common case.
> > + */
> > + if (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;
> > +
> > + if (!ret) {
> > + /*
> > + * SVN successfully updated.
> > + * Let users know when the update was successful.
> > + */
> > + pr_info("SVN updated successfully\n");
> > + return 0;
> > + }
> > +
> > + /*
> > + * EUPDATESVN was called when EPC is empty, all other error
> > + * codes are unexpected.
> > + */
> > + ENCLS_WARN(ret, "EUPDATESVN");
> > + return -EIO;
> > +}
> > +
>
> This patch alone generates below build warning (both w/ and w/o 'W=1'):
>
> khuang2@khuang2-desk:~/work/enabling/src/tip$ make
> arch/x86/kernel/cpu/sgx/ W=1
> DESCEND objtool
> CALL scripts/checksyscalls.sh
> INSTALL libsubcmd_headers
> CC arch/x86/kernel/cpu/sgx/main.o
> arch/x86/kernel/cpu/sgx/main.c:940:12: warning: ‘sgx_update_svn’ defined
> but not
> used [-Wunused-function]
> 940 | static int sgx_update_svn(void)
> | ^~~~~~~~~~~~~~
>
> Regardless of whether this warning is reasonable or not, it is a warning
> during
> build process which may impact bisect.
>
> You can silence it by annotating __maybe_unused attribute to
> sgx_update_svn() in
> this patch, and then remove it in the next one.
>
> But I am not sure whether it is necessary, though. We can merge the last two
> patches together. The ending patch won't be too big to review IMHO.
>
> We can even merge patch 3 together too. The reason is current changelog of
> that
> patch doesn't explain why we only define that two error codes (or return
> values)
> but not others, which makes that patch *ALONE* un-reviewable without
> looking at
> further patches. That being said, it's fine to me we keep patch 3 alone, but
> it's better to do some clarification in changelog.
>
> But just my 2 cents. Since Dave/Ingo/Jarkko are all on this thread, I'll
> leave
> this to them.
Dave, do you have a strong opinion on this?
