From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 439A1C433E2 for ; Thu, 17 Sep 2020 16:16:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EFDF7206D4 for ; Thu, 17 Sep 2020 16:16:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728347AbgIQQQT (ORCPT ); Thu, 17 Sep 2020 12:16:19 -0400 Received: from foss.arm.com ([217.140.110.172]:48608 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728246AbgIQQP3 (ORCPT ); Thu, 17 Sep 2020 12:15:29 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DD34D11D4; Thu, 17 Sep 2020 09:14:36 -0700 (PDT) Received: from [10.37.8.97] (unknown [10.37.8.97]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BC3BF3F68F; Thu, 17 Sep 2020 09:14:33 -0700 (PDT) Subject: Re: [PATCH v2 22/37] arm64: mte: Add in-kernel MTE helpers To: Catalin Marinas , Andrey Konovalov Cc: Dmitry Vyukov , kasan-dev@googlegroups.com, Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <4ac1ed624dd1b0851d8cf2861b4f4aac4d2dbc83.1600204505.git.andreyknvl@google.com> <20200917134653.GB10662@gaia> From: Vincenzo Frascino Message-ID: <9ef0a773-71f0-c1d6-b67e-ccf7d8bcbbe6@arm.com> Date: Thu, 17 Sep 2020 17:17:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200917134653.GB10662@gaia> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/17/20 2:46 PM, Catalin Marinas wrote: >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c >> index 52a0638ed967..e238ffde2679 100644 >> --- a/arch/arm64/kernel/mte.c >> +++ b/arch/arm64/kernel/mte.c >> @@ -72,6 +74,52 @@ int memcmp_pages(struct page *page1, struct page *page2) >> return ret; >> } >> >> +u8 mte_get_mem_tag(void *addr) >> +{ >> + if (system_supports_mte()) >> + asm volatile(ALTERNATIVE("ldr %0, [%0]", >> + __MTE_PREAMBLE "ldg %0, [%0]", >> + ARM64_MTE) >> + : "+r" (addr)); > This doesn't do what you think it does. LDG indeed reads the tag from > memory but LDR loads the actual data at that address. Instead of the > first LDR, you may want something like "mov %0, #0xf << 56" (and use > some macros to avoid the hard-coded 56). > Seems I can't encode a shift of 56 neither in mov nor in orr. I propose to replace both with an and of the address with itself. This should not change anything. Thoughts? >> + >> + return 0xF0 | mte_get_ptr_tag(addr); >> +} >> + >> +u8 mte_get_random_tag(void) >> +{ >> + u8 tag = 0xF; >> + u64 addr = 0; >> + >> + if (system_supports_mte()) { >> + asm volatile(ALTERNATIVE("add %0, %0, %0", >> + __MTE_PREAMBLE "irg %0, %0", >> + ARM64_MTE) >> + : "+r" (addr)); > What was the intention here? The first ADD doubles the pointer value and > gets a tag out of it (possibly doubled as well, depends on the carry > from bit 55). Better use something like "orr %0, %0, #0xf << 56". > -- Regards, Vincenzo