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X-CSE-ConnectionGUID: 8iU+d7pJS+GzfIsceoOXvw== X-CSE-MsgGUID: FA3au3edSMaf6nGzvtoMnw== X-IronPort-AV: E=McAfee;i="6800,10657,11491"; a="58367593" X-IronPort-AV: E=Sophos;i="6.16,304,1744095600"; d="scan'208";a="58367593" Received: from fmviesa001.fm.intel.com ([10.60.135.141]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jul 2025 10:54:07 -0700 X-CSE-ConnectionGUID: qj+onFWGSruvJttldkNTHw== X-CSE-MsgGUID: ACVIvgoaSp2UW5ySgWYfhw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,304,1744095600"; d="scan'208";a="187402341" Received: from spandruv-mobl4.amr.corp.intel.com (HELO [10.125.111.20]) ([10.125.111.20]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jul 2025 10:54:07 -0700 Message-ID: <461a33d3-f91a-4dd3-bb97-048670530b25@intel.com> Date: Fri, 11 Jul 2025 10:54:06 -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 v7 5/5] x86/sgx: Enable automatic SVN updates for SGX enclaves 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, dionnaglaze@google.com, bondarn@google.com, scott.raynor@intel.com References: <20250711165212.1354943-1-elena.reshetova@intel.com> <20250711165212.1354943-6-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: 8bit On 7/11/25 09:50, Elena Reshetova wrote: > == Background == > > ENCLS[EUPDATESVN] is a new SGX instruction [1] which allows enclave > attestation to include information about updated microcode SVN without a > reboot. Before an EUPDATESVN operation can be successful, all SGX memory > (aka. EPC) must be marked as “unused” in the SGX hardware metadata > (aka.EPCM). This requirement ensures that no compromised enclave can > survive the EUPDATESVN procedure and provides an opportunity to generate > new cryptographic assets. > > == Patch Contents == > > Attempt to execute ENCLS[EUPDATESVN] every time the first file descriptor > is obtained via sgx_(vepc_)open(). In the most common case the microcode > SVN is already up-to-date, and the operation succeeds without updating SVN. > If it fails with any other error code than SGX_INSUFFICIENT_ENTROPY, this > is considered unexpected and the *open() returns an error. This should not > happen in practice. On contrary, SGX_INSUFFICIENT_ENTROPY might happen due > to a pressure on the system's DRNG (RDSEED) and therefore the *open() can > be safely retried to allow normal enclave operation. The effort to add paragraphs would be appreciated. > int sgx_inc_usage_count(void) > { > - atomic64_inc(&sgx_usage_count); > - return 0; > + int ret; ... For what it does sgx_inc_usage_count() is seriously hard to parse and complicated. Three logical atomic ops *and* a spinlock? Wouldn't this suffice? Just make 'sgx_usage_count' a normal integer and always guard it with a the existing lock: int sgx_inc_usage_count(void) { int ret; guard(mutex)(&sgx_svn_lock); if (sgx_usage_count++ == 0) return sgx_update_svn(); return 0; } Yeah, it makes the fast path a spinlock instead of an atomic_inc, but it's still the same number of atomic ops in the end. Isn't that a billion times more readable? It barely even needs commenting. What am I missing?