From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757560AbdEKPyd (ORCPT ); Thu, 11 May 2017 11:54:33 -0400 Received: from foss.arm.com ([217.140.101.70]:50100 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757467AbdEKPyb (ORCPT ); Thu, 11 May 2017 11:54:31 -0400 Subject: Re: [PATCHv2] arm64/cpufeature: don't use mutex in bringup path To: Mark Rutland , marc.zyngier@arm.com References: <1494514878-26878-1-git-send-email-mark.rutland@arm.com> <498b2e16-538a-d5ea-7843-2ebbff2007df@arm.com> <20170511153719.GB19626@leverpostej> Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, bigeasy@linutronix.de, catalin.marinas@arm.com, peterz@infradead.org, tglx@linutronix.de, will.deacon@arm.com From: Suzuki K Poulose Message-ID: <232510f0-115e-b2c6-022f-03efd2606d56@arm.com> Date: Thu, 11 May 2017 16:54:27 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170511153719.GB19626@leverpostej> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/05/17 16:37, Mark Rutland wrote: > On Thu, May 11, 2017 at 04:15:38PM +0100, Suzuki K Poulose wrote: >> On 11/05/17 16:01, Mark Rutland wrote: >>> +static inline bool cpus_have_const_cap(int num) >>> +{ >>> + if (static_branch_likely(&arm64_const_caps_ready)) >>> + return __cpus_have_const_cap(num); >>> + else >>> + return cpus_have_cap(num); >> >> We use cpus_have_const_cap() from hyp code, via has_vhe() and we could potentially >> try to access unmapped kernel data from hyp if we fallback to cpus_have_cap(). >> However, it looks like we have already set arm64_const_caps_ready, so should not >> hit it in practise. May be we could add a stricter version of the helper ? >> >> static inline cpus_have_const_cap_strict(int num) >> { >> BUG_ON(!static_branch_likely(&arm64_const_caps_ready); >> return __cpus_have_const_cap(num); >> } > > Just to check, is that the only user of cpus_have_const_cap() at hyp? Uh, no we have one more, via system_supports_fpsimd() in __actvate_traps. Suzuki > > If so, I can do something like the above, patching to use > it for has_vhe(). > > We don't have a BUG handler at hyp, but that should trigger a hyp panic, > which I guess is good enough. > > Marc, thoughts? > > Thanks, > Mark. >