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[2001:8b0:10b:1231::1]) by mx.google.com with ESMTPS id e1si4749756wrd.58.2019.02.05.05.30.15 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 05 Feb 2019 05:30:15 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) client-ip=2001:8b0:10b:1231::1; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=PoMhzwSc; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=CVKHIuEvj5JGw+bPxiuecR8XPRMXnKXfH5LmqCODJr0=; b=PoMhzwScDlbzVjbkRBMfS4MZr XfllCw3u9d26TcsNbDc093sC1RxuPXDZdQHSK2vTbLzwL0ojT3aZp0xe4o9jyt6A0d5fQOCSYHUih 6CF3lbljAfVseZghqn6Pau0P5tXLAO6zQQcAGTTjRx862pUtQgZIEQwub/rYZPsmd6yqPnj0TGBVs ElzmBbTUGISW5G0NVPgVofxdS7/o1cgNo8R1wO/E43lLvGAy0Ljfc0lF85dD8t8x/RDAE29wcXiT0 YTsQpytF2iY8zJOfEEnJwEpajF0ODa1Q2SMkWVJhldOFAkFR5r6YXvmenPbdZ7AVxX3z7cOOCcMxP ophLotiNQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gr0nT-00047L-1s; Tue, 05 Feb 2019 13:29:55 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id C67B82029F1D6; Tue, 5 Feb 2019 14:29:53 +0100 (CET) Date: Tue, 5 Feb 2019 14:29:53 +0100 From: Peter Zijlstra To: Borislav Petkov Cc: Rick Edgecombe , Andy Lutomirski , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, Thomas Gleixner , Nadav Amit , Dave Hansen , linux_dti@icloud.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, akpm@linux-foundation.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, will.deacon@arm.com, ard.biesheuvel@linaro.org, kristen@linux.intel.com, deneen.t.dock@intel.com, Nadav Amit , Kees Cook , Dave Hansen , Masami Hiramatsu Subject: Re: [PATCH v2 06/20] x86/alternative: use temporary mm for text poking Message-ID: <20190205132953.GF17582@hirez.programming.kicks-ass.net> References: <20190129003422.9328-1-rick.p.edgecombe@intel.com> <20190129003422.9328-7-rick.p.edgecombe@intel.com> <20190205095853.GJ21801@zn.tnic> <20190205113146.GP17528@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190205113146.GP17528@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 05, 2019 at 12:31:46PM +0100, Peter Zijlstra wrote: > In general, text_poke() cannot fail: > > - suppose changing a single jump label requires poking multiple sites > (not uncommon), we fail halfway through and then have to undo the > first pokes, but those pokes fail again. > > - this then leaves us no way forward and no way back, we've got > inconsistent text state -> FAIL. Note that this exact fail scenario still exists in the CPU hotplug code. See kernel/cpu.c:cpuhp_thread_fun(): /* * If we fail on a rollback, we're up a creek without no * paddle, no way forward, no way back. We loose, thanks for * playing. */ WARN_ON_ONCE(st->rollback);