Commit 33200303 authored by Marc Zyngier's avatar Marc Zyngier Committed by Will Deacon
Browse files

arm64: cpufeature: Add an early command-line cpufeature override facility 



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: default avatarMarc Zyngier <maz@kernel.org>
Acked-by: default avatarDavid Brazdil <dbrazdil@google.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210208095732.3267263-14-maz@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent f6f0c436

arch/arm64/kernel/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

arch/arm64/kernel/head.S

+1 −0
Original line number Diff line number Diff line
@@ -438,6 +438,7 @@ SYM_FUNC_START_LOCAL(__primary_switched) 
#endif

	mov	x0, x21				// pass FDT address in x0

	bl	early_fdt_map			// Try mapping the FDT early

	bl	init_feature_override		// Parse cpu feature overrides

#ifdef CONFIG_RANDOMIZE_BASE

	tst	x23, ~(MIN_KIMG_ALIGN - 1)	// already running randomized?

	b.ne	0f

arch/arm64/kernel/idreg-override.c

0 → 100644
+150 −0
Original line number Diff line number Diff line 
// 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 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];

	int len;



	len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",

		       reg->name, reg->fields[f].name);



	if (!parameqn(cmdline, opt, len))

		return -1;



	return kstrtou64(cmdline + len, 0, v);

}



static void __init match_options(const char *cmdline)

{

	int i;



	for (i = 0; i < ARRAY_SIZE(regs); i++) {

		int f;



		if (!regs[i]->override)

			continue;



		for (f = 0; strlen(regs[i]->fields[f].name); f++) {

			u64 shift = regs[i]->fields[f].shift;

			u64 mask = 0xfUL << shift;

			u64 v;



			if (find_field(cmdline, regs[i], f, &v))

				continue;



			regs[i]->override->val  &= ~mask;

			regs[i]->override->val  |= (v << shift) & mask;

			regs[i]->override->mask |= mask;



			return;

		}

	}

}



static __init void __parse_cmdline(const char *cmdline)

{

	do {

		char buf[256];

		size_t len;

		int i;



		cmdline = skip_spaces(cmdline);



		for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);

		if (!len)

			return;



		len = min(len, ARRAY_SIZE(buf) - 1);

		strncpy(buf, cmdline, len);

		buf[len] = 0;



		if (strcmp(buf, "--") == 0)

			return;



		cmdline += len;



		match_options(buf);



	} while (1);

}



static __init void parse_cmdline(void)

{

	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {

		const u8 *prop;

		void *fdt;

		int node;



		fdt = get_early_fdt_ptr();

		if (!fdt)

			goto out;



		node = fdt_path_offset(fdt, "/chosen");

		if (node < 0)

			goto out;



		prop = fdt_getprop(fdt, node, "bootargs", NULL);

		if (!prop)

			goto out;



		__parse_cmdline(prop);



		if (!IS_ENABLED(CONFIG_CMDLINE_EXTEND))

			return;

	}



out:

	__parse_cmdline(CONFIG_CMDLINE);

}



/* Keep checkers quiet */

void init_feature_override(void);



asmlinkage void __init init_feature_override(void)

{

	int i;



	for (i = 0; i < ARRAY_SIZE(regs); i++) {

		if (regs[i]->override) {

			regs[i]->override->val  = 0;

			regs[i]->override->mask = 0;

		}

	}



	parse_cmdline();



	for (i = 0; i < ARRAY_SIZE(regs); i++) {

		if (regs[i]->override)

			__flush_dcache_area(regs[i]->override,

					    sizeof(*regs[i]->override));

	}

}