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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1isP6Q-0005cu-53; Fri, 17 Jan 2020 10:43:46 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1isP6I-0005cT-UD for linux-arm-kernel@lists.infradead.org; Fri, 17 Jan 2020 10:43:44 +0000 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 270A711D4; Fri, 17 Jan 2020 02:43:38 -0800 (PST) Received: from [10.162.16.56] (a075563-lin.blr.arm.com [10.162.16.56]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9DB033F68E; Fri, 17 Jan 2020 02:43:34 -0800 (PST) Subject: Re: [PATCH v3 06/16] arm64: enable ptrauth earlier To: Catalin Marinas References: <1576486038-9899-1-git-send-email-amit.kachhap@arm.com> <1576486038-9899-7-git-send-email-amit.kachhap@arm.com> <20200116162414.GF10277@arrakis.emea.arm.com> From: Amit Kachhap Message-ID: <2d14a778-5fdf-7735-6fb1-57de3aa3e275@arm.com> Date: Fri, 17 Jan 2020 16:13:06 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20200116162414.GF10277@arrakis.emea.arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200117_024339_062367_30ADBD14 X-CRM114-Status: GOOD ( 14.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kees Cook , Suzuki K Poulose , Ard Biesheuvel , Richard Henderson , Kristina Martsenko , James Morse , Ramana Radhakrishnan , Mark Brown , Vincenzo Frascino , Will Deacon , Dave Martin , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 1/16/20 9:54 PM, Catalin Marinas wrote: > On Mon, Dec 16, 2019 at 02:17:08PM +0530, Amit Daniel Kachhap wrote: >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index 5aaf1bb..c59c28f 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -13,6 +13,7 @@ >> #include >> #include >> >> +#include >> #include >> #include >> #include >> @@ -713,6 +714,7 @@ secondary_startup: >> * Common entry point for secondary CPUs. >> */ >> bl __cpu_secondary_check52bitva >> + bl __cpu_secondary_checkptrauth >> mov x0, #ARM64_CPU_BOOT_LATE >> bl __cpu_setup // initialise processor >> adrp x1, swapper_pg_dir >> @@ -831,6 +833,24 @@ __no_granule_support: >> early_park_cpu CPU_STUCK_REASON_NO_GRAN >> ENDPROC(__no_granule_support) >> >> +ENTRY(__cpu_secondary_checkptrauth) >> +#ifdef CONFIG_ARM64_PTR_AUTH >> + /* Check if the CPU supports ptrauth */ >> + mrs x2, id_aa64isar1_el1 >> + ubfx x2, x2, #ID_AA64ISAR1_APA_SHIFT, #8 >> + cbnz x2, 1f >> +alternative_if ARM64_HAS_ADDRESS_AUTH >> + mov x3, 1 >> +alternative_else >> + mov x3, 0 >> +alternative_endif >> + cbz x3, 1f >> + /* Park the mismatched secondary CPU */ >> + early_park_cpu CPU_STUCK_REASON_NO_PTRAUTH >> +#endif >> +1: ret >> +ENDPROC(__cpu_secondary_checkptrauth) > > Do we actually need to park secondary CPUs early? Let's say a secondary > CPU doesn't have PAC, __cpu_setup won't set the corresponding SCTLR_EL1 > bits and the instructions are NOPs. Wouldn't the cpufeature framework > park it later anyway? In the current cpufeature framework, such missing cpufeature in secondary cpu will lead to kernel panic (inside check_early_cpufeatures) and not cpu offline. However Kristina in her RFC V2 [1] added such feature to park it. Later for moving the enabling ptrauth to assembly this work got dropped. Suzuki provided the template code for doing that [2]. Later James suggested to do this like existing __cpu_secondary_check52bitva which parks the secondary cpu very early and also to save wasted cpu cycles [3]. So your question is still valid that it can be done in cpufeature. Let me know your opinion that which one is better. [1]: https://lore.kernel.org/linux-arm-kernel/20190529190332.29753-4-kristina.martsenko@arm.com/ [2]: https://lore.kernel.org/linux-arm-kernel/9886324a-5a12-5dd8-b84c-3f32098e3d35@arm.com/ [3]: https://www.spinics.net/lists/arm-kernel/msg763622.html > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel