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Fri, 05 Feb 2021 16:42:17 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l84BT-00078O-Mh for linux-arm-kernel@lists.infradead.org; Fri, 05 Feb 2021 16:42:16 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1B2E464EDE; Fri, 5 Feb 2021 16:42:14 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1l84BP-00CILP-M7; Fri, 05 Feb 2021 16:42:11 +0000 MIME-Version: 1.0 Date: Fri, 05 Feb 2021 16:42:11 +0000 From: Marc Zyngier To: Will Deacon Subject: Re: [PATCH v6 12/21] arm64: cpufeature: Add an early command-line cpufeature override facility In-Reply-To: <20210205163521.GA22665@willie-the-truck> References: <20210201115637.3123740-1-maz@kernel.org> <20210201115637.3123740-13-maz@kernel.org> <20210205163521.GA22665@willie-the-truck> User-Agent: Roundcube Webmail/1.4.10 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, dbrazdil@google.com, alexandru.elisei@arm.com, ardb@kernel.org, jingzhangos@google.com, pajay@qti.qualcomm.com, psodagud@codeaurora.org, sramana@codeaurora.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210205_114215_897253_C0BD3184 X-CRM114-Status: GOOD ( 23.60 ) 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 , Jing Zhang , Prasad Sodagudi , Srinivas Ramana , Suzuki K Poulose , Catalin Marinas , linux-kernel@vger.kernel.org, Ard Biesheuvel , James Morse , Julien Thierry , Ajay Patil , kernel-team@android.com, David Brazdil , Alexandru Elisei , kvmarm@lists.cs.columbia.edu, 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+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021-02-05 16:35, Will Deacon wrote: > On Mon, Feb 01, 2021 at 11:56:28AM +0000, Marc Zyngier wrote: >> In order to be able to override CPU features at boot time, >> let's add a command line parser that matches options of the >> form "cpureg.feature=value", and store the corresponding >> value into the override val/mask pair. >> >> No features are currently defined, so no expected change in >> functionality. >> >> Signed-off-by: Marc Zyngier >> Acked-by: David Brazdil >> Reviewed-by: Catalin Marinas >> --- >> arch/arm64/kernel/Makefile | 2 +- >> arch/arm64/kernel/head.S | 1 + >> arch/arm64/kernel/idreg-override.c | 164 >> +++++++++++++++++++++++++++++ >> 3 files changed, 166 insertions(+), 1 deletion(-) >> create mode 100644 arch/arm64/kernel/idreg-override.c >> >> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile >> index 86364ab6f13f..2262f0392857 100644 >> --- a/arch/arm64/kernel/Makefile >> +++ b/arch/arm64/kernel/Makefile >> @@ -17,7 +17,7 @@ obj-y := debug-monitors.o entry.o irq.o >> fpsimd.o \ >> return_address.o cpuinfo.o cpu_errata.o \ >> cpufeature.o alternative.o cacheinfo.o \ >> smp.o smp_spin_table.o topology.o smccc-call.o \ >> - syscall.o proton-pack.o >> + syscall.o proton-pack.o idreg-override.o >> >> targets += efi-entry.o >> >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index d74e5f84042e..3243e3ae9bd8 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -435,6 +435,7 @@ SYM_FUNC_START_LOCAL(__primary_switched) >> >> mov x0, x21 // pass FDT address in x0 >> bl early_fdt_map // Try mapping the FDT early >> + bl init_feature_override >> bl switch_to_vhe >> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) >> bl kasan_early_init >> diff --git a/arch/arm64/kernel/idreg-override.c >> b/arch/arm64/kernel/idreg-override.c >> new file mode 100644 >> index 000000000000..d8d0d3b25bc3 >> --- /dev/null >> +++ b/arch/arm64/kernel/idreg-override.c >> @@ -0,0 +1,164 @@ >> +// SPDX-License-Identifier: GPL-2.0 >> +/* >> + * Early cpufeature override framework >> + * >> + * Copyright (C) 2020 Google LLC >> + * Author: Marc Zyngier >> + */ >> + >> +#include >> +#include >> +#include >> + >> +#include >> +#include >> + >> +#define FTR_DESC_NAME_LEN 20 >> +#define FTR_DESC_FIELD_LEN 10 >> + >> +struct ftr_set_desc { >> + char name[FTR_DESC_NAME_LEN]; >> + struct arm64_ftr_override *override; >> + struct { >> + char name[FTR_DESC_FIELD_LEN]; >> + u8 shift; >> + } fields[]; >> +}; >> + >> +static const struct ftr_set_desc * const regs[] __initconst = { >> +}; >> + >> +static char *cmdline_contains_option(const char *cmdline, const char >> *option) >> +{ >> + char *str = strstr(cmdline, option); >> + >> + if ((str == cmdline || (str > cmdline && isspace(*(str - 1))))) >> + return str; >> + >> + return NULL; >> +} >> + >> +static int __init find_field(const char *cmdline, >> + const struct ftr_set_desc *reg, int f, u64 *v) >> +{ >> + char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2], *str; >> + size_t len; >> + >> + snprintf(opt, ARRAY_SIZE(opt), "%s.%s=", reg->name, >> reg->fields[f].name); >> + >> + str = cmdline_contains_option(cmdline, opt); >> + if (!str) >> + return -1; >> + >> + str += strlen(opt); >> + len = strcspn(str, " "); > > I'm absolutely terrified of string parsing in C, but just wondering why > you > only ignore literal spaces here. I _think_ the full-fat cmdline parsing > uses > isspace() to delimit the options. That's clearly an oversight, as I use a more complete set of characters for the rest of the option splicing. I also think that with the way things are now parsed (options being extracted early and trimmed), we can drop this altogether. > Would it be possible to reuse any of the logic over in parse_args() to > avoid > having to roll this ourselves? Maybe. I need to have a look. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel