linux-kernel - RE: [PATCH v6 4/5] x86/sgx: Implement ENCLS[EUPDATESVN]

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Message-ID: <DM8PR11MB5750BBF67BA29F9E2A7AAA77E766A@DM8PR11MB5750.namprd11.prod.outlook.com>
Date: Thu, 29 May 2025 13:41:54 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: "Hansen, Dave" <dave.hansen@...el.com>
CC: "Raynor, Scott" <scott.raynor@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "mingo@...nel.org" <mingo@...nel.org>, "Scarlata,
 Vincent R" <vincent.r.scarlata@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"jarkko@...nel.org" <jarkko@...nel.org>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>, "Cai, Chong" <chongc@...gle.com>,
	"bondarn@...gle.com" <bondarn@...gle.com>, "linux-sgx@...r.kernel.org"
	<linux-sgx@...r.kernel.org>, "dionnaglaze@...gle.com"
	<dionnaglaze@...gle.com>, "Huang, Kai" <kai.huang@...el.com>
Subject: RE: [PATCH v6 4/5] x86/sgx: Implement ENCLS[EUPDATESVN]


> >
> > +/**
> > + * 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@...ang2-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?