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From: Will Deacon <will@kernel.org>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	David Brazdil <dbrazdil@google.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Jing Zhang <jingzhangos@google.com>,
	Ajay Patil <pajay@qti.qualcomm.com>,
	Prasad Sodagudi <psodagud@codeaurora.org>,
	Srinivas Ramana <sramana@codeaurora.org>,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kernel-team@android.com
Subject: Re: [PATCH v6 12/21] arm64: cpufeature: Add an early command-line cpufeature override facility
Date: Fri, 5 Feb 2021 16:35:21 +0000	[thread overview]
Message-ID: <20210205163521.GA22665@willie-the-truck> (raw)
In-Reply-To: <20210201115637.3123740-13-maz@kernel.org>

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 <maz@kernel.org>
> Acked-by: David Brazdil <dbrazdil@google.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> ---
>  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 <maz@kernel.org>
> + */
> +
> +#include <linux/ctype.h>
> +#include <linux/kernel.h>
> +#include <linux/libfdt.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/setup.h>
> +
> +#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.

Would it be possible to reuse any of the logic over in parse_args() to avoid
having to roll this ourselves?

Will

  reply	other threads:[~2021-02-05 20:35 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-01 11:56 [PATCH v6 00/21] arm64: Early CPU feature override, and applications to VHE, BTI and PAuth Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 01/21] arm64: Fix labels in el2_setup macros Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 02/21] arm64: Fix outdated TCR setup comment Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 03/21] arm64: Turn the MMU-on sequence into a macro Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 04/21] arm64: Provide an 'upgrade to VHE' stub hypercall Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 05/21] arm64: Initialise as nVHE before switching to VHE Marc Zyngier
2021-02-05 12:01   ` Hector Martin 'marcan'
2021-02-05 14:04     ` Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 06/21] arm64: Move VHE-specific SPE setup to mutate_to_vhe() Marc Zyngier
2021-02-03 21:13   ` Will Deacon
2021-02-04  9:30     ` Marc Zyngier
2021-02-04  9:34       ` Will Deacon
2021-02-04  9:50         ` Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 07/21] arm64: Simplify init_el2_state to be non-VHE only Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 08/21] arm64: Move SCTLR_EL1 initialisation to EL-agnostic code Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 09/21] arm64: cpufeature: Add global feature override facility Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 10/21] arm64: cpufeature: Use IDreg override in __read_sysreg_by_encoding() Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 11/21] arm64: Extract early FDT mapping from kaslr_early_init() Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 12/21] arm64: cpufeature: Add an early command-line cpufeature override facility Marc Zyngier
2021-02-05 16:35   ` Will Deacon [this message]
2021-02-05 16:42     ` Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 13/21] arm64: Allow ID_AA64MMFR1_EL1.VH to be overridden from the command line Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 14/21] arm64: Honor VHE being disabled from the command-line Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 15/21] arm64: Add an aliasing facility for the idreg override Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 16/21] arm64: Make kvm-arm.mode={nvhe, protected} an alias of id_aa64mmfr1.vh=0 Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 17/21] KVM: arm64: Document HVC_VHE_RESTART stub hypercall Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 18/21] arm64: Move "nokaslr" over to the early cpufeature infrastructure Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 19/21] arm64: cpufeatures: Allow disabling of BTI from the command-line Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 20/21] arm64: Defer enabling pointer authentication on boot core Marc Zyngier
2021-02-01 11:56 ` [PATCH v6 21/21] arm64: cpufeatures: Allow disabling of Pointer Auth from the command-line Marc Zyngier

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