From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Fri, 11 Apr 2014 17:00:29 +0100 Subject: [RFC PATCH] uprobes: copy to user-space xol page with proper cache flushing In-Reply-To: <20140411153249.GZ11096@twins.programming.kicks-ass.net> References: <20140409184507.GA1058@redhat.com> <5347655B.3080307@linaro.org> <20140411.003636.272212797007496394.davem@davemloft.net> <20140411145625.GA27493@redhat.com> <20140411152207.GA28188@redhat.com> <20140411153249.GZ11096@twins.programming.kicks-ass.net> Message-ID: <20140411160028.GR16119@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Apr 11, 2014 at 05:32:49PM +0200, Peter Zijlstra wrote: > On Fri, Apr 11, 2014 at 05:22:07PM +0200, Oleg Nesterov wrote: > > And I am just curious, why arm's copy_to_user_page() disables premption > > before memcpy? > > Without looking, I suspect its because the VIVT caches, they need to get > shot down on every context switch. So... let's think about that for a moment... if we have a preemption event, then that's a context switch, which means... No, this is obviously not the reason, because such an event on a fully VIVT system would result in the caches being flushed, meaning that we wouldn't need to do anything if we could be predicably preempted at that point. -- FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly improving, and getting towards what was expected from it.