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X-CSE-ConnectionGUID: ZXKvTPmjT7exNqrjRl5xYw== X-CSE-MsgGUID: CLLSTA1jS8asnsWSQ3dxXA== X-IronPort-AV: E=McAfee;i="6800,10657,11508"; a="67788385" X-IronPort-AV: E=Sophos;i="6.17,255,1747724400"; d="scan'208";a="67788385" Received: from orviesa007.jf.intel.com ([10.64.159.147]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Aug 2025 10:12:59 -0700 X-CSE-ConnectionGUID: 4W1TGk90Rq6w0Asfd2mdcw== X-CSE-MsgGUID: azLkx13EQluNt3pEM9IGsQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.17,255,1747724400"; d="scan'208";a="163624955" Received: from aschofie-mobl2.amr.corp.intel.com (HELO [10.125.109.249]) ([10.125.109.249]) by orviesa007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Aug 2025 10:12:59 -0700 Message-ID: <96866c15-2eb1-4df4-9e63-dfd5e40ecb91@intel.com> Date: Fri, 1 Aug 2025 10:12:58 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN] To: Elena Reshetova Cc: jarkko@kernel.org, seanjc@google.com, kai.huang@intel.com, mingo@kernel.org, linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, asit.k.mallick@intel.com, vincent.r.scarlata@intel.com, chongc@google.com, erdemaktas@google.com, vannapurve@google.com, bondarn@google.com, scott.raynor@intel.com References: <20250801112619.1117549-1-elena.reshetova@intel.com> <20250801112619.1117549-6-elena.reshetova@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit The changelog is missing a tidbit about the fact that this is still dead code until sgx_inc_usage_count() gets a real implementation. 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..."); > + * 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. > + * 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. > + * 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; } > + ENCLS_WARN(ret, "EUPDATESVN"); > + return -EIO; > +} > + > int sgx_inc_usage_count(void) > { > return 0;