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X-CSE-ConnectionGUID: jwdyKsaQSIKynbwA1yZROw== X-CSE-MsgGUID: SrEPvrxhQdaZY5PKLh8T+g== X-IronPort-AV: E=McAfee;i="6800,10657,11491"; a="64952869" X-IronPort-AV: E=Sophos;i="6.16,311,1744095600"; d="scan'208";a="64952869" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by orvoesa103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jul 2025 06:54:55 -0700 X-CSE-ConnectionGUID: YftOcVh/SKqmm3qTBCsFgw== X-CSE-MsgGUID: 0wUaOB3eRBq8RYZIXbPsIw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,311,1744095600"; d="scan'208";a="157040592" Received: from dwesterg-mobl1.amr.corp.intel.com (HELO [10.125.111.82]) ([10.125.111.82]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jul 2025 06:54:52 -0700 Message-ID: <2cd81800-12ba-460e-ac28-4532d0be1ec9@intel.com> Date: Mon, 14 Jul 2025 06:54:50 -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: "Reshetova, Elena" Cc: "jarkko@kernel.org" , "seanjc@google.com" , "Huang, Kai" , "mingo@kernel.org" , "linux-sgx@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "Mallick, Asit K" , "Scarlata, Vincent R" , "Cai, Chong" , "Aktas, Erdem" , "Annapurve, Vishal" , "dionnaglaze@google.com" , "Bondarevska, Nataliia" , "Raynor, Scott" References: <20250711165212.1354943-1-elena.reshetova@intel.com> <20250711165212.1354943-6-elena.reshetova@intel.com> <461a33d3-f91a-4dd3-bb97-048670530b25@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 On 7/14/25 00:35, Reshetova, Elena wrote: > I think you put it: this would require a spinlock in the fast path and > *in theory* if we are running many many concurrent enclaves can create > contention FWIW, my mental model is that spinlocks that are held for short periods of time are pretty much the same cost as an atomic under contention. If there are lots of users, the cost of moving the cacheline for the atomic or the spinlock dominates everything else. It doesn't matter whether that cacheline is an atomic_t or spinlock_t. The only difference is that there is _visible_ spinning for a spinlock.