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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id 14sm1966746wmv.36.2018.12.06.08.28.58 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 06 Dec 2018 08:28:59 -0800 (PST) Date: Thu, 6 Dec 2018 17:28:57 +0100 From: Ingo Molnar To: Nadav Amit Cc: Ingo Molnar , Steven Rostedt , LKML , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Borislav Petkov , Andy Lutomirski , Dave Hansen , Peter Zijlstra , Damian Tometzki , linux-integrity , LSM List Subject: Re: [PATCH v7 08/14] x86/ftrace: Use text_poke_*() infrastructure Message-ID: <20181206162857.GA119243@gmail.com> References: <20181205013408.47725-1-namit@vmware.com> <20181205013408.47725-9-namit@vmware.com> <25B84F01-DB4C-4957-9703-769CCC9794BB@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <25B84F01-DB4C-4957-9703-769CCC9794BB@vmware.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Nadav Amit wrote: > > On Dec 4, 2018, at 5:34 PM, Nadav Amit wrote: > > > > A following patch is going to make module allocated memory > > non-executable. This requires to modify ftrace and make the memory > > executable again after it is configured. > > > > In addition, this patch makes ftrace use the general text poking > > infrastructure instead ftrace's homegrown text patching. This provides > > the advantages of having slightly "safer" code patching and avoiding > > races with module removal or other mechanisms that patch the kernel > > code. > > > > Cc: Steven Rostedt > > Signed-off-by: Nadav Amit > > --- > > arch/x86/kernel/ftrace.c | 74 +++++++++++++--------------------------- > > 1 file changed, 23 insertions(+), 51 deletions(-) > > Steven Rostedt pointed that using text_poke() instead of > probe_kernel_write() would introduce considerable overheads. Running: > > # time { echo function > current_tracer; } > > takes 0.24s without this patch and 0.7s with. I don’t know whether to > consider it “so bad”. Obviously we can introduce a batching mechanism and/or > do some micro-optimization (the latter will not buy us much though). This should definitely not regress, so can we try the batching approach? Thanks, Ingo