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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id m6sm2926767wmc.32.2019.05.08.04.32.41 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 08 May 2019 04:32:42 -0700 (PDT) Date: Wed, 8 May 2019 13:32:39 +0200 From: Ingo Molnar To: "Reshetova, Elena" Cc: David Laight , Andy Lutomirski , Theodore Ts'o , Eric Biggers , "ebiggers@google.com" , "herbert@gondor.apana.org.au" , Peter Zijlstra , "keescook@chromium.org" , Daniel Borkmann , "linux-kernel@vger.kernel.org" , "jpoimboe@redhat.com" , "jannh@google.com" , "Perla, Enrico" , "mingo@redhat.com" , "bp@alien8.de" , "tglx@linutronix.de" , "gregkh@linuxfoundation.org" , "Edgecombe, Rick P" , Linus Torvalds , Peter Zijlstra Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall Message-ID: <20190508113239.GA33324@gmail.com> References: <303fc4ee5ac04e4fac104df1188952e8@AcuMS.aculab.com> <2236FBA76BA1254E88B949DDB74E612BA4C6C2C3@IRSMSX102.ger.corp.intel.com> <2e55aeb3b39440c0bebf47f0f9522dd8@AcuMS.aculab.com> <20190502150853.GA16779@gmail.com> <20190502164524.GB115950@gmail.com> <2236FBA76BA1254E88B949DDB74E612BA4C6F523@IRSMSX102.ger.corp.intel.com> <2236FBA76BA1254E88B949DDB74E612BA4C760A7@IRSMSX102.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2236FBA76BA1254E88B949DDB74E612BA4C760A7@IRSMSX102.ger.corp.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Reshetova, Elena wrote: > CONFIG_PAGE_TABLE_ISOLATION=n: > > base: Simple syscall: 0.0510 microseconds > get_random_bytes(4096 bytes buffer): Simple syscall: 0.0597 microseconds > > So, pure speed wise get_random_bytes() with 1 page per-cpu buffer wins. It still adds +17% overhead to the system call path, which is sad. Why is it so expensive? Thanks, Ingo